Extra: Otherworld, Manifestation

To those unfamiliar with To Aru Majutsu no Index, the easiest way to explain Dark Matter is this: 『Otherworld Terraforming』. In other words, anything goes.

And so, the clock’s hands tick forward, leading to the moment war breaks out.

Kakine Teitoku.

Kihara Amata.

Kihara Bayuri.

Kihara Gensei.

Four "abnormal" beings gather, at the threshold of a grotesque conflict.

Chapter 2: I Won’t Choose Between Two Options – PHASE-NEXT.
Extra: Otherworld, Manifestation

『──Gagahh, K-Kakine-san!?』

At that moment, the tiny mic in Kakine’s ear picked up Yobou’s voice.

When he had tried to hold back the intruders earlier, Yobou had seemingly been defeated and put down by the Seventh-ranked. But it looked like he’d managed to recover here and now.

"Yobou? You alright?"

『Y-yeah, more or less. I’ve been hearing about the situation over there from our subordinates who were monitoring things, so I have a decent grasp of it.』

"You can see what’s going on here? It’s a real mess, though."

『There are drones set up for the tournament broadcast. Since they can film from long range, if we hijack their controls we can use them to monitor the situation too. …If you need another hand, I can jump in as well.』

"Nah, don’t. Quit it. You wouldn’t stand a chance."

『……,』

Kakine had said it lightly, but the air on the other side of the comm instantly grew taut. He had just stepped on the guy’s pride, but even so, Kakine still had the leisure to smirk.

"Oh? You mad?"

『……!! Nngh, n-no…』

"My bad. Didn’t mean it that way."

Spreading his wings, Kakine locked eyes with the old man standing before him.

The elder, whose body shimmered with a formless haze like sugar dissolving into the air, waited patiently for their conversation to end.

"That guy’s output is enough to trigger localized earthquakes. For now he’s either messing around or too focused on his experiments, so he’s only been using it as basic kinetic energy… but really, it’s just that he doesn’t know the ‘recipe.’"

Originally, Kihara Gensei hadn’t possessed the move called Unrestricted Poltergeist. Rather, it was something the ‘Kiharas’ had devised after noticing his multi-skill talents, and he had simply incorporated it into his arsenal.

But at the same time, it was hard to believe that Kihara Gensei’s ingenuity ended there.

Now imagine, if someone like Yobou—who could generate a wide range of effects with the same telekinesis—were on the same battlefield?

Gensei would no doubt draw infinite inspiration from Yobou’s style and evolve his own power further.

The risk of that far outweighed any benefit of having Yobou here.

"Still, even if it’s just a small comfort… I want you to handle pulling our guys out of here. Even grunts still have their uses. I’m leaving it to you."

『……! Got it!!』

Once the call was cut, Kakine refocused on Gensei.

Gensei stroked his chin with his remaining left hand, leisurely listening the whole time. The other two Kiharas also refrained from trying to exploit the opening, maintaining their silence.

No.

There was no opening.

If this had been someone less seasoned, like Souji or Enshuu, they might have thrown in a "test strike" and gotten hammered by the devastating counter. But veterans like the Kiharas knew better. They could clearly sense the unseen force field swirling around Gensei, always ready to lash out with a violent response like reactive armor against any attack.

"All done? Then let’s resume the experiment, shall we?"

"Ah—sorry for keeping you waiting, old man."

Kakine’s reply sounded genuinely apologetic, but only for an instant.

"I already finished on my end."

Kyugaaaaaahhhhhh!!!!

The ground at Gensei’s feet suddenly erupted.

It wasn’t an explosion.

The concrete rose, discolored, and—spewed molten magma.

In one word: 『Eruption』.

"Hyoh!? This is… turning the ground into a volcano!? It’s my first time observing the Second-ranked ability up close, but this is bizarre!! He’s transforming the geological composition into one that shouldn’t even exist!?"

"If that’s enough to make your eyes pop, you’re in for a rough ride, gramps."

But the anomaly didn’t stop there.

Naturally, Gensei leapt to safety from the magma. Yet right in front of his eyes, the red-hot torrent solidified mid-splash into stone. And then, with a crushing blow from Kakine’s wings—

Dobaaaaaaahhhhh!!!!

Fragments of shattered rock turned into thousands of tiny blades, all rushing toward Gensei.
Faced with an overwhelming torrent of destruction that could not be avoided by mere dodging, Gensei played his card: Chaotic Release Poltergeist.

Naturally, the mass of energy capable of even causing earthquakes swallowed the storm of blades without difficulty, yet Kakine’s grin didn’t waver.

"Kinetic energy in its plainest form sure is convenient, huh? But precisely because of that, its movements are easy to predict."

There was no sound.
A gray blade, slipping through the gaps of the Poltergeist’s 『power』, descended like a guillotine and sliced off Gensei’s left arm at the elbow.

"My Dark Matter, the Unoriginal Substance, can produce about 1,700 different transformation patterns."

"As expected of the Number Two… If the Number One weren’t around, I would’ve loved to use you as research material, you knowー"

"……Looks like I still haven’t cut off enough of your limbs yet."

GOSSH!!
A violent gale roared forth from Kakine’s wings. Wriggling like a dragon and moving on its own, it targeted Gensei. It was no longer something as simple as a mere 『storm』…

"Was it 1,700 patterns? It’s true, that ability contains limitless potential, you knowー"

Gensei’s severed left arm struck the ground on its own, rebounding into the air.

"But in reality, the choices Kakine-kun can make in the spur of the moment are far fewer than 1,700. And if you’re reacting to my actions as input, that number narrows even further—at most, about 200 in an instant, I’d sayー?"

The severed arm floating in the air unleashed a gale from its palm.

Compared to Kakine’s, its destructive power was on another level. This storm, a living thing beyond reason, should have swallowed everything, tearing the old man’s body to pieces with the very power of the atmosphere.

"Something like that is easy enough to predict, you knowー"

BOBAHHH!!!!

The storm was split in two at its center, like a snake blown apart by dynamite in its belly. It was Gensei’s own air current, calculated down to perfection, that had forced such an outcome.

And the anomaly didn’t stop there.

The backlash from the sundered storm now turned on its creator, Kakine.

"This bastard…!?"

Completely unexpected.
Caught by surprise, Kakine’s body was flung through the air like a brittle branch.

Victory—
That was the certainty carried by such a strike. Yet at that very moment, Gensei noticed it.

A blade had already pierced his torso without him realizing it.

"You probably thought… you had read me like an open book…"

Kakine, collapsed on the ground, forced the words out.

"But why didn’t you consider that even that assumption was me leading you along?"

Yes.
Everything had been in Kakine’s hand from the start.

If I attack this way, my opponent will anticipate the next move. Then, in response, they’ll counter with this.
Laid out in words it sounds simple, like a word game. But Kakine had constructed it with frightening precision. For an esper who could twist the world into the unknown through abnormal phenomena, controlling the entire field according to his will was as easy as breathing.

"Im…possible…? My forcefield defense was definitely…?"

"Yeah, that’s right. That’s why I prepared it. A blade that only slices through human flesh and passes harmlessly through everything else."

Anything goes.

That was the lawless absurdity embodied by the man who bore the title of Academy City’s Number Two.

One decisive strike. Kakine had landed a fatal blow, and his wings retracted.
Gensei sank to his knees, powerless—

"So you thought it would end with just that muchー?"

KUGAHHH!!!

Even as he collapsed, his legs alone propelled him into a sudden leap.

"The hell!? This guy, the attack definitely…"

"It landed, alright! But… tch, damn old geezer, so your torso’s packed full of machinery too, huh!?"

The explanation was simple.
If a blade only cut flesh and passed through all else—then if the area cut was a mechanical replacement, naturally, it would inflict no damage.

"I’ve taken a lot of damage from accidents during experiments, you knowー. By now, my body’s practically a showcase of substitute technologies."

"I figured as much. I fought you once before, after all, so I’ve got a decent idea of the tricks you’ve got up your sleeve."

As Kakine fell back, another stepped forward to take his place—Byouri, in her wheelchair, facing Gensei.

Moving swiftly on spider-like mechanical arms of mysterious technology, Byouri had more than just mobility in her arsenal.

From above, countless meteors rained down.

Of course, the invisible forcefield surrounding Gensei warded them off. Yet the sudden assault from outside his awareness forced him to halt.

"They’re drones, you know. The ones used to broadcast the Daihaseisai."

Byouri’s revelation was disarmingly simple.
Or perhaps it was her way of saying that such a small trick couldn’t possibly reveal the true extent of her arsenal.

"……So you hacked into the Daihaseisai Executive Committee’s servers? Naughty girlー"

"Of course not. That was remote control, you know? It’s just like a computer virus. If you send out the right control signals, you can hijack them easilyー"

And that was all.

For a Kihara, such a simple tactic might even feel unsatisfying. But the essence of a Kihara wasn’t about defining themselves by the complexity of the science they used.

It was about how to abuse the science birthed by their brilliant intellect.

In other words—the application of converting the potential energy intended for aerial broadcasting into a direct attack. Simple, and utterly malicious.

That straightforward move possessed such raw power that even Gensei, with his earthquake-spawning strength, had to actively defend against it—or else it would punch straight through.

And that wasn’t the end.

"Next, why don’t we try this one?"

Just as Gensei was handling the sporadic meteors raining down from hijacked drones, it happened.

A runaway bus came barreling over the rubble, charging straight at him.

"Hyoh!?"

Of course, something like that was well within Gensei’s ability to stop. But that wasn’t the real problem.

"……The bus’s network system should be completely separate from the drones, thoughー. Could it be, just like with biological viruses, that infection spreads through direct contact between machines?"

"As expected of the old monster. I didn’t think you’d leave any of your cards hidden."

Byouri grinned wide.

"In this day and age, every machine has both computation and communication functions built-inー"

That was all the explanation she gave. But it was enough for everyone present to understand completely.

If you hack into the computation functions, it’s theoretically possible to rewrite them at the OS level. From there, you can modify the communication functions at will, allowing devices on different networks to be hacked as if they were linked. In other words, machine virus contact infection becomes reality.

"Source: Thriller."

It was just like zombies multiplying endlessly.

"Of course that includes cyborg bodies tooー"

In this era, cyborgs were also clusters of computational devices.

From safeties to prevent self-injury, to posture control, to the transmission of electrical signals—computation governed everything. And cyborgs often communicated with each other as well. The severed left arm that had moved on its own earlier—that was the trick.

"Hyoh!?"

Gensei’s left arm suddenly tried to gouge out his right eye all by itself.

It was absurd.

To rob a cyborg body of its own control—that was outrageous. But Gensei—

"This is rather… entertaining, you knowー"

GICHH!
Using his swirling forcefield with delicate precision, he restrained his own rampaging body.

But of course, it was a perilous balancing act. Like trying to build a sandcastle with an excavator—one mistake, and his body could be minced to pieces.

Yes.
If anything went wrong.

"Yo, what’s the matter? You not gonna play with me too?"

Behind the struggling Gensei stood a man.

Wearing a savage grin that seemed to rip his face apart—Kihara Amata. His action was extremely simple.

He whistled.

Just that.

And it triggered a dramatic change.

The sound waves, generating a special airflow, disrupted the forcefield. The delicate balance that maintained it collapsed, and Gensei’s body was instantly twisted tight, like a rag being wrung out.

"O-OooooOOOOOOoooooOOOOHHHH!?!?!"

"You’re not done yet, are ya!!!??"

Kihara Amata didn’t stop.

On the contrary, he strode forward with absolute confidence that a counterattack would come, weaving between the still-raining drone meteors and showers of molten lava.

"You’ve hidden it well enough, but I can tell from the whirring of your drives and the way you move. Which parts of you are flesh, and which are machine, huh?"

He raised only two fingers.

Right hand shaped into a weapon, sharp as a fork. And then—

He gouged into Kihara Gensei’s flank with his bare hand.

For a moment, there was silence. Then, from Gensei’s abdomen, red-black fluid began to spill.

"Gu-OOOOAAAAAAaaaaaAAAAAAHHHHHHHHHH!?!?"

"GYAA-HHAHAHAHAHAHAHAHAHA!!!! Thanks for the wonderful performance!! No time to rest, the second movement’s about to begin!!!"

"──If things had gone that easily, it sure would’ve been nice, huhー?"

The next moment.

Kihara Gensei—who should have just had his side gouged open—moved as if nothing had happened, his left hand sweeping up with flawless grace.

And then, with a single stormwind blast, Kihara Amata’s body was hurled through the air.

Hurled—no, it was more like he became a bullet. With that much force, Amata shot straight across the battlefield, skipping off the ground like a stone across water, bouncing shallowly again and again before vanishing into the rubble far away.

At the same time, the disorderly rampaging forcefield—used mostly to restrain Gensei’s own berserk body—returned to its original, fluid motion.

"……!? My body’s control… it’s—"

"My hand isn’t limited to the Poltergeist Unleash, you knowー"

A sharp crackle burst from his raised hand. Purple sparks flashed.

"Multiskill. Though, since there wasn’t a simple Electromaster lying around, I had to spend a little extra time building a detour for the circuitsー"

"……Yaaah, you really are a damn monster geezer, huh…!"

"Pathetic."

Spitting out that curse, Byouri kept her distance—only for Kakine Teitoku to suddenly step forward past her.

──The three of them may have had a common enemy, but that didn’t make them allies. That was why, so long as Gensei seemed confident enough to handle the situation, they stayed back. Watching in silence, careful not to get caught in the recoil of his counterblows.

And in the meantime, they observed the way his victims were crushed—turning that knowledge into a strategy to defeat him.

"Multiskill. Poltergeist Unleash. Cyborg substitute tech. …If those are the only tricks you’ve got, then sorry, but I’ll crush them all right now."

Kakine’s strike was simple.

He brought his wing down from above. That was it.

But that one strike already surpassed the speed of sound.

On top of that, the wings emitted radio waves that disrupted the functions of precision instruments. And the scattered feathers—shaped like brooms—carried soundwaves that generated specialized air currents.

10,368.

That was the number of distinct phenomena packed into this single attack.

"Th-this number…!? What is this…!?"

"Who ever said my one strike had to be just one strike?"

With a motion almost elegant in its simplicity, he swung his arm down.

And then, more than ten thousand simultaneous effects surged at Kihara Gensei.

"Guess you could say the first stage is cleared, huh?"

Unscathed.

…or at least, that’s what one might call it, though the sight was anything but. His right leg was petrified, and his remaining left arm was covered in strange crystalline thorns. Any superhuman movements befitting a cyborg were now beyond hope. But even so, an even greater threat remained.

The crackling sword of lightning.
It was not merely electrical discharge.
AIM.
What Fuse=Kazakiri wielded, he had summoned into his hand.

With that, he had cleaved through the nonexistent matter, Dark Matter.

"Tch…"

There was no choice but to reset the field here. Kakine understood as well. Charging in recklessly against "that" would mean more than just a painful counterattack.

"Oh-ho, look who finally made it back—only to turn into some kind of fancy-looking geezer."

From behind him came the voice of Kihara Amata. Looking back, Amata bore a few scrapes here and there, but no serious injuries. Most likely, he had minimized damage by precisely controlling his posture as he was blown away.

"So you’re alive. Perfect timing—lend me a hand."

"Hah? The hell are you babbling about?"

"Lend a hand to a 'Kihara'? That’s a strange request indeed."

The air between the two Kiharas bristled with tension at the unexpected proposal. In such cases, a "Kihara" would be the first to betray. A sudden request for cooperation carried a meaning akin to declaring, "I’m about to betray you and kill you."

"Not that I have any intention of lending a hand, though."

Despite those contradictory words, Kakine launched a probing strike at Gensei. The two Kiharas were the ones left confused. He asked for cooperation, only to admit he wouldn’t cooperate himself. Utterly incoherent.

"So you won’t lend a hand yourself, yet expect us to? Sounds like you’re telling us to become sacrificial pawns."

"Not 'sounds like.' That’s exactly what I’m saying."

Kakine declared flatly, without a hint of emotion.

"You think I’m joking? What makes you think you’re on equal footing with me? You’re not. You’re supposed to make me think you’re 'too valuable to waste.' That’s how hard you should be working to lend me a hand."

A simple "command," without any pretense of negotiation. The Kiharas’ response was just as simple.

"Gyahahahaha! This guy’s hilarious!"

"You sure are underestimating 'Kihara,' aren’t you?"

Bare hands.
Meteorites.

Each with their own brand of "science," they moved to kill Kakine Teitoku. No hesitation, no rational delay—just immediate action.

Kakine, too, turned the phenomena born from Dark Matter to his advantage, deflecting their attacks. A strike that had twisted its trajectory transformed its frictional heat into cold, becoming an icy meteor that froze Gensei’s leg like a stray shot.

Amata’s punch, absorbed by a feather, was released into the chaotic disturbance of a poltergeist field, tearing away force itself like a bird pecking at bread crumbs.

"…You bastard…"

"The Kihara clan was never suited for teamwork. That other Kihara I fought before, that 'Soji' or whatever, admired you, Amata-san, but still acted solo. But on the flip side, when it comes to in-fight brawling, you’re made for it. So the solution’s simple. I just set the stage so your in-fighting ends up looking like teamwork."

Anomalous science—swallowed whole by an otherworldly strategy. Before the mind of Academy City’s #2, cold sweat trickled down Kihara Byouri’s face.

"Whatever this 'Kihara' is supposed to be, you really think you can measure me with the yardstick of some deranged scientist? You’re underestimating Dark Matter way too much."

"Hyoh-hoh-hoh. That’s quite the 'teamwork' you’ve got. As expected of the second-choice spare plan. Your compatibility with Kihara isn’t as good as the first-choice main plan or the exceptional bonus plan, but still impressive enough to make me take notice."

"Don’t get carried away. Your analysis is already finished."

The moment Kakine said that, the sword of lightning in Gensei’s hand crumbled to dust, turned into stone.

"…Hyoh?"

"Sheesh. To think you’d try to wedge an anomaly into the world while leaving me out of it—that’s some 'science' you’ve got. Thanks to you, it took me a bit of time to fix the broken gears."

Until now, Dark Matter had not been at its full potential.

That was because Gensei’s summoning of Fuse=Kazakiri had flooded the area with AIM, and that AIM had interfered with Dark Matter, disrupting its proper activation.

In terms of operational capacity, Kakine had only been running at 30%. That was the true extent of his specs so far.

But if things ended there, he would hardly be worthy of calling himself a Level 5. Even while fighting, Kakine had succeeded in factoring AIM into his calculations and predicting the surrounding phenomena accordingly.

…It was a state of mastery that, for a reincarnator, would require professional guidance and endless effort to finally achieve. Yet Academy City’s #2 executed it effortlessly.

From the crumbled stone remains of the lightning sword, greenery sprouted forth, vines wrapping around Gensei’s body. Blossoms burst into bloom, only to detonate in miniature explosions, searing his flesh.

Amata did not stop either. Somehow having procured an iron pipe, he advanced toward the immobilized Gensei, striking the ground as he moved. Yet it was not reckless bravado. From the sparks of the pipe came writhing tendrils of flame that lashed and tormented Gensei.

"Oh? Now that’s interesting. So you can use it like this too, huh?"

"…What was that?"

──Dark Matter.
Instead of treating it as a mere "universal substance," he was leveraging the warped physical laws themselves, twisted at the particle level. Amata had stepped into a domain that not even Kakine Teitoku had reached before—and he laughed.

…A "Kihara."
This was the "true nature" of the clan he had scorned moments earlier.

And of course, there was still one person who had not yet entered the fray.

She too was a professional dwelling in the shadows of this city—

Zuzun…

With a quake in the earth, a "giant" appeared.

"Ooh, it took quite some time, but I somehow made it just in time, didn’t I?"

Manipulating the countless interlocked machines that made up the hulking figure, the woman in the wheelchair spoke with a sly smile.

If there existed a machine virus capable of endlessly multiplying its hosts, then what would be the most hopeless "tactic" one could employ with it?
Importing countless specialized devices to create pseudo-omnipotence? That was certainly one option.

But there was something even simpler, even more overwhelming, even more despair-inducing.

That was "absolute mass."

If one could control a vast multitude of machines at will, there was no need to overcomplicate things. Just gather them all into one and smash it against the enemy. That alone was enough to crush earthquakes, endless abilities, even scientific angels alike—reducing them all to nothing.

An attack that robbed one of the very will to resist.

"Resignation."

That was the true specialty of Kihara Byouri.

"Origin—'Spectacle.'"

"O. Oooh, oooooOOOOOOOOOOOOOOOOH!?!?!"

Gensei roared instinctively, trying to hold back the massive blow. But not a single person present intended to let that opening go. Against the two who wielded otherworldly logic, his body accumulated damage, bit by bit—

──And then.

Crack. Half of Kihara Gensei’s face shattered away.

His visage split like the shell of an egg, his body on the verge of being crushed. Yet even so, Gensei laughed.

He laughed, and spoke.

"…It… is… done."