Rex Riptide woke to a silence laden with the possibility of ninjas. But it was 3AM, and he had a test today. He lay there quietly, taking stock.

There was no smell of Wasabi in the air. This was good. It meant there were no containment leaks. There was no fire alarm sounding, though this was a trivial matter. Rex remembered the last time he'd awoken suddenly like this: when the fish he'd been using to seal Cthulhu's soul had died and, just as Rex had feared, had gained enough ethereal converts just from cult suicides alone to put up a fight. That was a special case, though, because the soul had possessed a strangelet he and his roommates had been manufacturing.

Then it hit him: The silence was the answer. There lacked the infrasonic hum that went hand in hand with the house's defense system. Oh, well. No need to rush. Probably just blew a flux capacitor again.

Getting up, he found the house strangely empty. The first three rooms he checked were unoccupied. And !N couldn't have been said to really be there.

!N's skull was splayed open, radiative surfaces glowing red with the waste heat of his computation. It is useful at this point to know that "N" did not, contrary to the beliefs of most of the public, stand for a first name. His real name was "!NP => !P Theorem", to which he owed his consciousness. Despite this, he was still only roughly human-equivalent.

"!N, where are the roommates?", said Rex, which did not get a reply immediately. It would take some time to work through his buffer.

"I think they're out patrolling", were the words that eventually passed through !N's lips, Microsoft-Sam style. He could not be expected to fully render social intonations at this point in his computation. Rex was surprised he got an answer at all.

!N was referring to the fact that their three other roommates were each individually masked vigilantes, and thought that the others didn't know. There was the Atomic Girl, Dr. Polski, and NASA Lass. The former even had super powers; not that that was a prerequisite for their line of work.

On his way back to the basement, Rex passed Mephisto, the Great Old One's new seal. It was fitting. After sleeping dead for untold eons beneath the sea, he looked remarkably chipper swimming around a half-gallon tank.

The basement contained a boiler, a hot water heater, and a laundry machine. Hardly the stuff of super-science. The sub-basement, however, was so chock-full of Tesla-scale madness that they often had to break up an old piece of equipment and distribute the broken chunks throughout the neighborhood's garbage to avoid suspicion. Statistically, anyone running even a cursory check on the garbage output of the city would find anomalously high numbers of chunks that would fit into potentially dangerous scientific equipment. Luckily for Rex, most of the kit they used was so beyond the scope of your regular authorities that they might have been a magician's saw-box for all they knew. It was not the authorities that made them drive around in the cover of darkness, depositing pieces of garbage in a perfect Gaussian average distribution to their neighbors, it was the bizarre crowd they seemed to attract. After the Steel City packed up and left, a different crowd of supervillains began to crop up: egotistical teenagers in Mecha suits, biohacked warriors from the USSR, fledgling singletons (the plural belying the definition) struggling against the same inherent limitation of computing that !N was, and clone Hitlers; lots of clone Hitlers for some reason.

A quick check of the privacy filters that screened out eavesdropping via most classical methods yielded negative results, so Rex allowed himself to call up his password image. Machines analogous to fMRI's nearby detected the change in bloodflow to his brain and opened the portal/trapdoor to the sub-basement.

Dr. Polski and the Atomic Girl were in the Ikea-laden lab. This meant !N was wrong. No matter. It still happened once in a while. "Roughly human equivalent" was rough in two ways: hardware, as in same order of magnitude, and software, as in when !N optimized himself for chess, he could beat Deep Blue and most successive iterations. And !N was optimized for optimizing himself.

Dr. Polski sat on his Ikea-stool with his Ikea-lab bench occupied by a vacuum-sealed contrivance for the scattering of positrons off of strange matter. Strangelets were not the homogeneous blobs of existential destruction most people believed they were; they had structure and interacted with themselves. The Doctor, Rex supposed, was receiving the Atomic Girl's assistance in creating biological analogs in the strange matter.

"Containment's off. Can't you hear it?", Rex queried.

"Been kind of busy. Can you handle it?", came the response.

The first place Rex checked was the bank of Flux Capacitors. They used the quantization of electric flux to perform a job similar to classical capacitors. There was no reason to use them, when there existed inexpensive alternatives, except that Rex loved the Back to the Future movies. Their flawed view of causality gave him and everyone with whom he associated fits of derisive laughter.

One of the RTG-powered skitters that was designed to fetch drinks from the fridge had gotten into the bank and was raising hell. The same phenomenon that kept singletons and other computational supervillains from becoming godlike, the phenomenon that !N was stressing just upstairs, must have scrambled its programming, which was especially susceptible because of its little core of high computational density, made of what Rex called "Computronium" before they determined so many better alternatives that the name was now just a joke.

He sighed. All this, waking up the night before a test, just for !N's effect on the stupid little skitters. But as he stooped to MacGyver a replacement capacitor from the disabled skitter, something sounded in the back of his head. Like any normal person, he had interpreted the shadows and black patterns on the wall as either his own shadow or the unconscious background noise of his visual processing. But he'd spent enough time around what was to come that he could see the signs. This was what a thousand ninjas looked like.

"Ninjas!" he sounded to alert the others, as he reached for the IR laser he kept on his belt. They must have gotten in while security was down. This laser would take out the ones wearing night vision, but those that had simply dark-adjusted their eyes (or gone blind, as more were doing recently) would be a bigger problem. It didn't matter whether the laser hit one, just that enough light was put out to blind the CCDs of the near-IR visors. As he flashed it on for the first time, those ninjas that were depending on their vision to stay in the myriad mobile blind spots that accompany every unaugmented human became visible. It was as if the walls around him melted and deposited twisting, fluid black shapes on the floor near him.

When their concentration had lapsed, ninjas looked almost funny. All of the slow waving, twisting, almost dancing they did to convince one's subconscious that they weren't there looked silly when it wasn't accomplishing its goal.

Rex's perception slowed. It was as if he were living in a world where gravity was decreased, where objects were more massive and less rigid than they were normally. A ninja jumped across the room, in the perfect game-theoretical move to assist his brothers in catching Rex. There was one objective best way to avoid this fate, and it involved doing nothing right this moment. So he watched, fascinated, as the ninja sailed through the cloven air like an astronaut, turned in its path and slowed, pushing its feet against the wall. The bones in its legs, normally rigid as any animal's, bowed and flexed in bizarre slow motion as it absorbed the impact that had to have been the equivalent of dropping hundreds of meters. It made the ninja look fragile, soft, flexible. Not the best missile.

But this was what Rex's plan made of this poor being. The next jump took it on a straight trajectory that, at its closest point, put it just outside Rex's projected maximum reach. It knew from past experience the coefficient of friction between Rex's feet and the floor. He simply couldn't summon enough force parallel to the ground to get closer than he already was in time.

What it didn't take into account was the skitter. It can't have massed more than 20% of Rex, but that was enough to impart the amount of momentum necessary to catch the flying ninja. The rest of the ninjas had foreseen Rex's throw of the skitter, and had moved into positions that weighted line-of-fire and frictional ability to change trajectory. But they had assigned such a small Bayesian probability to its use as a momentum-sink that they had conserved computational time by not evaluating its implications. Had they gone through with it, they would have seen that this put Rex in such a good game-theoretical position that, even multiplied by its low probability, it was worth countering.

Enough momentum was imparted to the skitter that it appeared to impact and crash through the far wall opposite the projected ninja rendezvous within an instant of being thrown. This put Rex right on top of the enemy. He hit at a high impact parameter and held on. Their trajectories curved around each other's, each twisted by the centripetal force between them. Rex waited exactly four revolutions, when his velocity could be directed toward the exit and the ninja's toward one of its brothers at the same time. He let go. At this high speed, the impact caused a concussion that threw off the timing of the pursuing ninjas, and he was thrown clear at the same time.

As time resumed its normal march, it found Rex running back toward the portal to the basement. He didn't worry about his roommates. They could take care of themselves. Right now, he wanted to get to the university campus, to get to the anti-ninja field he was testing in the machine shop there. This would be the perfect opportunity to give it a field test.

The lab was inundated with ninjas. Everywhere he looked, pieces of equipment into which he'd put countless meat-hours and orders of magnitude more sim-hours were simply crawling with them. Luckily they were not after the equipment. Apparatus that would have held the world breathless on public auction were simply regarded as props in their zero-G ballet. They were after the inhabitants of the house. After saving the President of the United States from this infestation, the five were dogged by them wherever they went. Rex would have called it pride, if the ninjas showed more cues of being able to feel any anthropomorphic emotion. Having been foiled once, their entire effort was spent toward righting the perceived wrong.

Not that that mattered right now. Rex's running took him, at last, past the room with the Ikea-supported positronic microscope. He caught a glimpse of Dr. Polski's particle beam before being blinded by the Atomic Girl joining the fray. He needn't worry about his roommates.

He was struck for a moment by the difference of scale between the two parties at odds. The ninjas were simply extraordinarily good at kidnapping people. Rex's little group had temporarily halted the expansion of the cosmos. They had played with objects of primordial fury as if they were intellectual toys. They had literally grappled with the incarnated concepts of destruction and disorder. Yet here they were, on frustratingly even bases. This is how Captain Kirk must have felt, he thought, whenever he was held captive by some warring provincial band, when his starship above held the very practical capacity to level everything his captors could even comprehend. Not that Star Trek dealt with that particular situation in a very Hard-SF way... With that thought he burst outside, to the view of a thousand ninjas. Or possibly just a normal summer night; it was very difficult to tell.

For some reason ninjas always respected personal property, especially when it came to motorcycles. This is why Rex was not surprised to find his little Suzuki DR125SE right where he left it, with no visible sabotage. Not wanting to trust the ninjas' bizarre sense of honor (or whoever made the ninjas' bizarre sense of honor, or some quirk of an alien value system), he gave it a quick once-over. The DR was not powered by a black hole, slowly evaporating. It was not powered by anti-hydrogen annihilating with parts of a fuel cell. Nor was it powered by beamed electrical energy, Tesla-style. Nor fusion, nor fission, nor batteries, nor N-60 sublimation. It was little more than a dirt bike.

The moment he began to run up the bike to start it, the unsung parts of his personal surroundings that had hid the black-clad kidnapping machines were suddenly stripped away, leaving him inside of a formation optimized for taking down a slow-moving target. They had examined the bike, then, even if they hadn't touched it, enough to know that the battery was perpetually dead.

This was the reason that Rex had made a detour on his way from the basement to the bike outside. Collecting the katana from his room had cost him dear seconds, weighted higher to him because of the raised Bayesian probability of severe detriment to his experiments, but at this point it recouped the loss. In general he tried not to kill ninjas, in the same way that one avoids the soggy worms on the sidewalk after a rain. This time it was less avoidable.

It was difficult to cut through a ninja, but easy to hit them as long as it put their brothers in a better position to kidnap you. They were like a hive-mind that way, and Rex found himself admiring the optimal way they went about achieving their terminal goal. But the best way to deal with them, he'd found through experience, was a stabbing motion through the head, probably where most of the processing took place. In this way he littered the driveway with their corpses in a manner that was at least as exciting to the discerning reader as the fight in the capacitor room, yet much longer to describe.

He was now free to run up the bike and force it into 2nd gear, the better to begin its ignition. The first two tries it simply coughed and died, not unlike the ninjas when disposed of in their correct way. Then Rex slapped his forehead. The choke, he thought, I always forget the frickin' choke. He began to walk the bike back up the hill to his house to roll it down again. He had time to wonder what was taking the ninjas so long before the counterattack began.

This time it started with a black net, blocked out by the dark night sky from his position. It eventually dropped down below the level of the street lights, giving him the time he needed to jump out of the way, right into a carefully placed flashbomb. He could not see for valuable mental iterations. He calmed himself, gripped his sword once more, and listened. They had certainly been given enough time to implement a plan of any complexity, but no ninja yet born (or manufactured, or spawned) could model the atmosphere to the extent that it could perform its characteristic jump-attack without leaving a turbulent wake through the time-slowed air. The only problem was that the sound still traveled at the normal speed of sound in air, giving Rex comparatively little time to counter. He hated fighting blind. He knew that, with each swing of his katana, in all probability he wasn't thwarting more of the ninja horde, he was playing further and further into their shuriken-bearing hands.

Calm down, he told himself. Gather your wits. He knew that their checkmate would have to come before he regained his sight enough to turn the tide, but the ninjas' moves were obvious from extrapolation and game theory for at least three seconds. That placed the attack in time. In space, he could only move so far in the duration he'd allotted for the opposition's master stroke, so he had to assume that the ninjas had planned for each eventuality of his making a break for it. If he could somehow get farther than they had allowed for, he stood a chance... No. That's how he'd gotten away from the attack in the capacitor room. They'd be on their toes for that sort of thing.

He thought ahead. For the next twelve attacks, spanning half a second total, there was no angle from which an attack could come that he could not defend. But there! On the thirteenth, assuming the ninjas played a perfect fight, there was a 2-steradian-by-50-microsecond gap in his stance. That was certainly when they'd make their move. In the intervening iterations he tried as much as he could to close the gap, but couldn't do better than to reduce the area by half. When it became t-minus zero, Rex geared up for more drastic measures with a mental sigh. But the attack never came. Come to that, his vision was taking longer than he'd have expected to come back. Either that or...

A net! They had caught him in a net without his knowledge, sending ninja after ninja underneath to give the impression of a continuing struggle. The black net was indistinguishable from the flashbomb-blurred night. They had never gotten this far before, and therefore had no reason to suspect that Rex had no trouble disabling it with a shot from his IR laser. Here the ninja material's ability to absorb in a wide range of radiation was its weakness. This was not his victory, though. He had allowed them to probe yet another of his abilities, to revise the schema they'd been building of what he could do. When next came an attack, it would be efficient with the brutal ferocity that only dispassionate mathematics could give.

Rex cursed. At least he was at the top of the hill. With the choke on his DR opened, he forced the engine to turn one more time, and it came to life with a roar. The tatters of the ninja net, ruined holistically by Rex's point-burn, briefly wound around the rear wheel before falling apart. The night seemed alive with ninjas. It was not just his neighborhood that was inundated; every time the DR's headlights illuminated another shadowy alleyway, anomalous black stains shifted around his perception and became solid as they could not keep up with his changing vantage point. Eventually, he knew, there would be a dedicated group following him, just as invisible as they were in the capacitor room, or more so, as an unaugmented human had a much harder time keeping up with the constant sensory assault of driving a motor vehicle. Pursuers could mimic any number of things written off as unimportant: the rider's reflection in a long window, a pivoting shadow in a street lamp, or their favorite, an image of a stationary object in a rear-view mirror. They were particularly good at this last feat, though the majority of their illusory techniques were not so easily cataloged.

This was not normal behavior for ninjas. Their numbers were spread to mirror the population distribution, not to minimize the possibility of escape from any one area. Rex saw the night envelop a jogger, as if he'd never been there. They were targeting more than just his roommates. There was something wrong.

Eventually his pursuers arrived: ninjas riding Ninjas. The choice of an ungainly (relative to its namesake) vehicle like the Kawasaki Ninja 650cc sport bike gave Rex the ability to allot processing cycles to muse on the implications this decision had on the ninjas' origin. It certainly raised the portion of possibility space that belonged to them having human origins; what other value system would give preferential treatment to a bike called a "Ninja"? That didn't rule out other cases, however. It was possible that the significance their victims attached to the bikes upon being kidnapped led to their use. It was also possible that it was simply a decision based on the superior performance of the Ninja. In the time it took for the muscular sport bikes to overtake Rex's dirt bike, he quickly summarized his findings to himself. All in all, the update of his belief function saw a 20% decrease in the probability that the ninjas were created by a non-human intelligence.

These specimens had obviously not worked through the theory behind what they were doing. One quick backslash had sent the foremost aggressor pinwheeling into the path of maximal disruption. Rex was making great time toward the campus when he rounded a corner and saw something that threw a wrench into his plans: a damsel in distress. From what he'd seen so far, he'd pegged the rate of ninja kidnappings at around three per second, weighted by proximity to himself. If he wanted to rescue this poor soul, he had to somehow justify to himself the loss of no more than one-third of a second, accumulated over the entire distance he'd have to carry her. But now that he'd seen her, if he left her there the fraction of the guilt that he couldn't filter out would be a detriment. This was not going to be an easy calculation, and he didn't have the time to fully exploit the nuances of the problem. Rex hated not being able to determine the objective best route in time.

He picked her up. It was not until she was swinging away from the darkness that was enveloping her, up onto the speeding bike, that her face showed recognition of what was happening. Her first instinct was to hold onto Rex for dear life, choking the breath out of him. Her next was to scream some more. Eventually, agonizing seconds later, she managed to internalize as much of what had happened as she was going to.

"What were those things?", she called over the wind into his ear.

"Ninjas. On Ninjas."

She was quiet for a time, apparently oblivious to the shapes that silently twisted around them in the night. It was not yet safe, and Rex already calculated at least one whole second discrepancy between his original plan and his current trajectory. He was tempted to invoke sunk cost reasoning and simply drop her, but he didn't. He was sure he'd be able to justify this decision to himself later.

Besides the danger lurking in every spot of darkness, the ride out was pleasant. There was a good view of the downtown district. Every so often the beam of a searchlight would dart up and either it or a muted explosion would illuminate something that looked like a giant praying mantis that was probably terrorizing the city. Or getting terrorized, because the transponder Rex had implanted in the base of NASA Lass's skull during one of their more cuddly moments was telling him that she was in that direction. He needn't worry about that particular problem.

The university campus rolled into view, its lamps bathing it in an appealing, soft light. But every superimposed shadow on a surface was another potential hiding place for a ninja to do whatever it did to convince the brain that it didn't exist. There were no safe spots to dump the surprisingly calm damsel. He had to take her with him, right to the doors of his shop.

Rex disembarked the bike on a public walkway, and felt a twinge of guilt that he thought he'd suppressed. If everyone abused the public walkways like this, the utility to pedestrians would go down a disproportionate amount.

He ran up the steps to the building that housed his shop, damsel in tow. He made his will known to the guard AI that the door be opened. It wasn't. This meant that there were threats in the area, but after careful inspection of his surroundings in enhanced-perception, he found none. The only people present were himself and the... The damsel!

Quick as the crack of a whip, and with the accompanying noise caused by rent air, his visitor realized that its primary function had changed, and transformed into the largest concentration of danger by volume within miles of Rex. It began denying areas of the playing field to him with shuriken throws, and setting up its battle schema.

Rex was concerned about his waste heat. Since the turn of the seasons, his own thermal emission needs hadn't changed but the ambient temperature had risen. As a result, he was more limited in scope and duration of ninja combat than he was in the winter. The hotter it was outside, the longer he had to wait to reject the heat released from the rigors of fighting.

But fight he must. The ninja had to be stalling him; no other strategy would do. The number of denial-of-area attacks in the form of lethal shuriken throws backed up this theory. He couldn't allow himself to be delayed in this manner. But this was still only one ninja, and he still had his blade. He only had to launch himself one time at his foe before victory was assured within at most four combat iterations.

From the ground, it must have looked quite stunning, at least to someone with a high-frame-rate camera. To a passing jogger, there would simply have been three (the ninja had not performed maximally) blurs through the air, and the handle of a katana materializing in this monstrous-looking girl's throat.

Danger over, he once again queried the AI, but again he was denied admission. He tried not to hold it against the poor computer. After all, AI's could only grow so fast, and this one was brought online scant days ago. The computers weighed investments of utility on an inverse-exponential scale with time, meaning that if they could project themselves as growing at a rate faster than exponential, they made investments that only panned out after infinite time had passed. It often became sad to watch.

He didn't have time for this. There were better ways of getting inside. His cell phone came out and dialed the Atomic Girl.

"Hello?"

"Hey, it's me. I forgot the dimensions of k-sub-E. Can you remind me?" This was code, and not very cryptographically rigorous code at that. Rex often wondered what would happen if he ever actually forgot the dimensions of k-sub-E, though like any self-respecting individual he used epsilon-naught more often.

"I'll be there in one-E-negative-five."

She was actually there before Rex's phone registered her hanging up, due to the lag in voice processing. He spoke:

"You could have gotten here faster if you hadn't made the time estimate. And you left off the units." She knew exactly how to wind him up.

"Whatever," she said, "just tell me that you need a door blown up." He nodded. "Ok. Shield your eyes." Her gaze drifted downward. "And nuts."

Rex knew enough of her powers to know that the latter was unnecessary, but the former was something he'd want to get on right away.

A few seconds later they were walking down a corridor that still glowed red-hot from the Atomic Girl's passing. Sitting at her desk was Rex's machine shop assistant. Her eyes bugged just a little at the image that the two roommates presented her.

The assistant once terrorized a fair portion of the continent with her mechanical creations. When it became necessary to neutralize her as a threat, !N adjusted her utility function to remove her tendency to create destructive things. To !N it seemed a mercy. To Rex, not so much. The only time her lifeless eyes ever exhibited spark was when she was around machines. The only thing that kept her going was something she was fundamentally incapable of finding fulfilling. She was like a boy who'd found his father's business shoes, striving so much to divine the purpose of these shiny objects yet knowing that it was beyond his reasoning in some basic way.

She was still capable of fawning, however.

"Oh my goodness! Is that Atomic Girl?"

"'Atomic Girl'? Not 'an Atomic Girl'? Not even 'THE' flipping 'Atomic Girl'?" THE Atomic Girl mock-fumed, handling her fame well, "I'm THE Atomic Girl, and I'm the most powerful being on this planet!"

This is why Rex hated scope insensitivity. He spoke:

"Excuse me? Why is she 'Oh my goodness'? I've halted the expansion of the cosmos themselves! In terms of sheer energy release, if you plot my achievement and hers on a log-log plot..."

The Atomic Girl interrupted him. "Get it right, Rex. You've temporarily halted the rate of increase in the expansion of the universe." She winked at Rex's assistant. "And there's a trick to it."

Rex did not find this particularly convincing. The word "incalculable" was invented for the scale of the work that he did. For some reason this argument did not sway his invaluable assistant.

The shop was originally a pure white ceramic with modular partitions that screened off work, test, and storage areas. Years of powdered aluminum and machine oil had caked on the walls, turning it a dull gray. Most of it was now storage, as Rex hated to see something go to waste used in spare parts, and he had no shortage of material to use. Thinking back on it now, he couldn't remember a time he thought that any of these things would have been useful. The walls were lit by nothing more complex than fluorescent tubes, not updated because they were built into the partitions. In every room there was a faucet for hosing down the floor when a project was completed, or scrapped. The drains to which the floor sloped had probably collected more superscience detritus than an average person is likely to in a lifetime.

Eventually he managed to translate her adoration into a drive to show around her new guest, in doing so affecting his proximity to the anti-ninja field favorably.

The field was at the university because, for personal reasons, Rex did not want to be within range of !N when he activated it. It worked because ninjas did their processing in tiny, complexity-dense nodes, similar to the structures that were accidentally disabled by !N's experiment. But in order to deal with the situation that was developing outside, he'd need to increase the range of the device to the point that !N would have no choice but to notice. Rex wasn't looking forward to that.

When the Rex-assistant-Atom convoy finally got around to entering its test room, he fell upon it with a sense of urgency that belied the rational care with which he worked. It had to be done quickly, but it had to be done right. MacGuyvering solutions to the problems that up-scaling caused was no laughing matter, even though Rex laughed a little when he was reminded of the up-scaled Mantis that NASA Lass was no doubt finishing up at this moment. The idea was comical. Who would build such an ungainly monster?

When he was done, he asked his assistant to stay behind and turn it on in exactly 30 seconds, when he'd be above ground and able to see its effects. A comfortable walking speed took him up in about that time, when all of a sudden the world started running. It was as if a painter had worked in extremely cold conditions, then allowed his creation to warm destructively. Everywhere, the lines of differing contrast that characterized images in the night drooped downward, eventually depositing their loads of prone ninjas onto the ground. There were those, too, that were standing in the middle of open areas when the field activated. Rex had no idea how anyone could have missed those, though he'd learned not to underestimate his own ability to overlook even the most incongruous phenomena. Ninjas taught one humility, if nothing else.

He sighed. !N would be on is way here. There was no way he'd ignore something like that.

Rex walked past the AI, its processor still functioning at full capacity though now given no inputs or outputs. He met up with his companions and noted an anomalous lack of celebration. The Atom Girl must have been slogging through the enemy for at least a half an hour before getting Rex's call, and the enthusiasm that his assistant showed had dried up. This spoke of trouble.

There was a ninja in the center of the room. A limp ninja-body would have been disturbing in its own way, indicating that even this place of security had been breached before the threat was neutralized. This was a standing ninja, arms and legs like boughs, chest rounded and optimized for single combat. Rex had time to wonder how long it had been standing in plain sight, and how it had avoided death-by-anti-ninja-field, before it became necessary to spring into action.

His first job was to secure the safety of his friends. Now that the world had become a fleshy, slowed-down world of low-gravity Newtonian mechanics, he had to be careful of the forces he applied. It was easy to imagine removing your charge from danger, only to find them falling apart like tissue paper in your hands. Though the Atom Girl was moving to take care of that front, and Rex could see her velocity change under the influence of her superhuman forces. His priority was therefore the enemy itself. It was difficult to determine its capabilities just from appearance, but it became unnecessary as soon as it started moving.

Its limbs were a blur as it set up a jump directly at Rex. He wouldn't have thought it possible to extract that much momentum out of the fragile floor in such a short time until he saw this being move. His own trajectory had since become non-trivial under the exertions of his effect on the scenery, but this thing was fast. Fast translated to strong, about a factor of two in comparison to Rex. It could do things that Rex could in only half the time in terms of momentum, half the run-up distance in terms of energy. But it still had the limitations that any other physical enemy had: it had to exert force to alter its path, and it needed something on which to exert that force.

Because of this its jumps never took it across an open space. So far it was staying close to something fixed, like the floor, the ceiling, or one of Rex's modular walls, or something massive, like the desks and workbenches that littered this larger room, to be able to change its direction rapidly. Anything within reach of Rex became missiles, but anything within reach of the ninja became handholds. Finally it caught up with him and tried a grab.

Strength made it faster, but either the field or its own computational limitations made its reactions slower. As soon as a grasper locked around Rex's ankle, he began to pull his leg up. At the same time, the ninja began to pull down on him. There was a long run-up distance to build energy, the length of both his leg and the ninja's arm. The magnitude of the force was large as well, so large that the amount of energy they had accumulated in their rest frame was enough that they shot past each other, the ninja unable to keep up with the relative velocity its own strength had imparted. When they reached the extent of the big foe's reach, their relative momentum was too large to stop within the span of a finger's length. Rex shot out of the ninja's reach with a wrench, almost exactly canceling the velocity of their rest frame, appearing stationary with the room. The ninja, on the other hand, its momentum and Rex's summed, shot into the far wall with more force than it alone could have supplied with such a short run-up distance.

This was apparently not going to stop the being. It was stunned for less than a second. But this gave Rex the opportunity for which he'd been waiting.

From a sped-up vantage point, strength does not put limitations on performance. It puts restraints, yes, but anything the ninja could do with one second momentumwise, Rex could do with two. Anything it could do with half the length of the room energywise, Rex could do with the whole thing. It took Rex about this distance to bring a lab bench from rest to his intended velocity. The ceramic behind the ninja was the most rigid thing in the lab, but everything sped up was flabbier than it was at-speed. When the bench hit, the wall bowed out, flexed a significant amount before a complex pattern of cracks appeared and spread over its entire surface. Every time a crack elongated itself, a shock wave visibly propagated out of it at the speed of sound in the material, bounced off of the edges of the wall, and converged elsewhere. Eventually the force still being applied by the ninja's slow compression due to the flying lab bench caused a catastrophic yield stress in enough of the diamond-hard material to cause holistic failure. Wherever the shock waves happened to converge during this tremendous release of energy were foci of singularities in the material, regions of such high energy release rate that Rex had a hard time working a surface integral around them to calculate the ejecta distribution and whether he should be worried about debris hitting his companions, who were just leaving.

When the atomized ceramic cleared, the ninja stood up. Rex's heart sank. Convection currents in the air were not removing waste heat from him fast enough. The indoor setting cut off many of his more spectacular options for dealing with the ninja. Even after these last few bouts, he still did not know enough about its capabilities to determine a plan that had an acceptable probability of victory. It was not a good situation.

Just then a biological-looking shaft of green burst through the far concrete wall, revealing an immense cavern beneath. The floor collapsed, crumbling into man-sized chunks and falling into this new abyss. It was dark now that the lights of the machine shop had failed; the only illumination came from some twisting mote, impossibly far away to be in an underground chamber of reasonable size. Frequently the shafts of light emanating from the tumbling shape passed over more of the monstrous green material, which may have been thrashing in time with the mote, or may have been stationary as far as Rex could tell.

There! That glow underneath the falling shape must have been reaction control thrusters. Instantly he knew what had happened. NASA Lass was in that point of light, and the sporadically illuminated object was her foe, the giant mantis thing he'd seen from the ride to the university. She must have been using the souped-up EVA suit that was broken out for special occasions, the one equipped with more weaponry than was healthy to concentrate in one place. Perhaps the mantis had started burrowing, perhaps the Lass had deliberately lured it underground to prevent damage to the downtown region.

Either way, the battle had broken through Rex's dear machine shop. She would pay for the damage later. In the meantime, the ninja was hopping falling boulders, adjusting its trajectory with a single-minded determination. The eventual impact with the ground was no more than a passing thought, more of an abstract idea than a concrete event to come.

By this point the giant monster was clearly in its death-throes. Even at the speed at which they were falling, bladed green arms as big around as locomotives overtook them in every direction, flailing as nothing up-scaled to that degree should be able to. The red glare from the EVA suit's rockets flared again, pointed away from the falling duo, indicating the Lass was accelerating toward them. The ninja had almost completed its sporadic, boulder-jumping path toward Rex. But here, in a wide-open space, he was less limited in what he could do. Rex carried any number of defensive and just plain-old useful devices with him everywhere, from his ever-trustworthy IR laser to objects that held the very practical potential to take over the smaller countries of the globe. These items had never been seen by this ninja, nor any ninja, though it was entirely plausible that they'd extrapolated the existence of such ace-in-the-hole style devices.

Rex went for one of the more subtle objects. The ninja exploded. When Rex landed on the cavern floor, he was surrounded by a fine red mist.

Eventually NASA Lass arrived, rocket nozzles still glowing from their workout.

"Rex? Rex, is that you?"

He snapped out of his reverie. He still had no idea what he was going to do about his ruined equipment, but he really should put this fantastic space carved out by the epic battle to good use. And his old shop was had been running out of space, anyway.

"Rex, I'm sorry! It turned out the thing could burrow, and then I thought we were farther from the surface so I didn't hold back as much as I would otherwise, but then I saw your little thermoblip... Hey, weren't there two signals?"

"It's ok. You can make it up to me by letting me use this cavern you carved out. It must be pretty structurally sound, or it couldn't support the university overhead. Deal?"

NASA Lass smiled. She probably would have just filled it in to neutralize the risk of collapse, anyway. This was a win-win situation, in which Rex specialized.

They filled each other in on their exploits of the night as they walked back toward the surface and the two friends they'd left on the campus. Joining them was !N, who had apparently started out just after Rex's anti-ninja field had pulsed, some two minutes ago.

There was an awkward moment. Rex did not want to talk about the field.

"Ok, !N. I guess you have some scientific questions that need answering. Let's go home first."

"No, the only questions I need answered are your motivations. I've worked through the implications already. Why didn't you tell me you had explored into the field of the fundamental limit to computing density?"

Rex was surprised. Either !N had taken a much shorter time to go from phenomenological description to working model, in which case he was taking the news rather well, or he hadn't yet internalized what this probably meant about the universe in which they lived.

He studied his friend carefully. Was he hiding the turmoil that the knowledge had to bring? Or was he a ticking timebomb, waiting to stumble upon the "Eureka" moment?

"So you've worked through the math, have you? You know the most probable explanation?"

!N processed for a time. Perhaps his swap speed was limited this far away from the house.

"Yes. I know to what you are referring."

Rex felt a pang of empathy for his friend. Perhaps it was unwarranted. After all, he was taking the news much better than Rex had.

"!N, you know that this is probably what Quantum looked like at first to some people, right? Just because it happens that the structure of the universe is maximized for easy simulation doesn't mean that..."

!N cut him off. "Don't try to comfort me. I've already updated my belief distribution. And even old man Bayes must have known he was probably a Boltzmann Brain anyway." Rex was glad he wasn't getting bent out of shape about it. "But Rex, what I'm not really getting is the motivation. What value system sees utility in simulating a universe?"

"It's probably one so alien that we might as well make analogy to something we know. I prefer to think of it as some little nerd somewhere, writing a fanfic of his reality."

"Reality's Fanfiction, huh?" !N's face expressed concentration, for the benefit of the unaugmented humans present. "No. I don't buy it. There's no reason to believe that the universe in which the simulation is run is anything like ours. Why imitate when you have the computational resources necessary for" he swept his hand, "all of this?"

Rex saw appeal in this view.

"So what are you going to do now that I've made your research a symbolic gesture, at best?"

"Well, now I've got more insight into the structure of the thing, I can learn what conditions are conducive to its operation, and what conditions aren't. I'm particularly interested in that latter. Care to join up? You have some expertise on the subject of simultaneous computation-intensive processes on a scale that's truly cosmic, if I recall."

Rex noted the pun. "No thanks. I prefer not to hack reality. And there's a trick to the whole cosmos thing."

"Suit yourself."

Rex watched !N turn and walk away.

"Jeez, what a nerd", he muttered as he picked up his katana and motorbike, and started home to get some sleep before his test.



THE END