Tsutsumi looked mildly annoyed by what Symboli Soji had just revealed, though not enough to act on it.
This was the world of Uma Musume and Kabuto. The Worms were their problem, not his.
He only killed that one because it copied him. The last idiot who dared to steal his face and memories had gone a step further and tried to pass themselves off as a Rider.
Left alone long enough, they might even start acting like Decade.
That alone was reason enough to erase them on sight.
Even so, Tsutsumi had no intention of getting directly involved. Worms, Riders, secret organizations, those were roadblocks Kabuto was meant to deal with. This was his story, not Tsutsumi's.
Unfortunately, things weren't that simple.
This was also Oguri's world.
Having the power to intervene and choosing to do absolutely nothing would just be irresponsible. He didn't like interfering, but he didn't like not doing anything knowing his sister might be harmed even more.
"As I've said already," Tsutsumi spoke calmly, breaking the silence. "I'm just the one who records the story. I won't directly help you unless you fail badly enough that I have to step in."
His gaze shifted to Soji.
"But since this is Oguri's world too, I can't just sit back and watch."
He paused for half a second.
"If you need help from me, just ask."
Soji tilted his head slightly, staring into Tsutsumi's piercing purple eyes.
"I don't need to take the hand of a devil to protect this world." He replied coldly.
Ignoring the worried looks from his sister and everyone else, Soji slowly raised his right index finger, pointing toward the ceiling.
"Grandmother said this: The whisper of the devil can sometimes sound like an angel's voice."
The meaning was obvious.
Symboli Soji didn't trust Tsutsumi Ryoko.
A few members of the Student Council glanced toward Rudolf, subtly urging her to talk sense into her brother. Rudolf didn't move.
She knew better than anyone.
As a Symboli, her brother's pride ran high. He believed he walked the path of heaven, and that it was his duty to rule everything beneath it. Once he decided something, he wouldn't bend easily.
"If that's your answer," Tsutsumi said evenly. "Then I guess we're done here."
He stood up and headed for the door, Oguri trailing right behind him.
Just before leaving, he stopped. Without turning back, he added one last thing.
"My offer still stands. Whether you use it or not is up to you."
Then he left the infirmary with Oguri followed closely.
The moment they stepped outside, Tsutsumi's horse ears reappeared atop his head, flicking slightly as the air changed.
"Tsu…" Oguri muttered quietly from behind him. "I'm hungry."
Tsutsumi: "..."
"…Of course you are."
...
After escorting his sister to the cafeteria and making sure she was fed, for the second time that day, Tsutsumi returned to his dorm room, expecting peace, quiet, and exactly zero surprises.
He got none out of three.
Agnes Tachyon was already inside, sitting at his desk as if it belonged to her. Several unfamiliar glass tubes were neatly arranged beside her, along with a notebook filled with cramped, barely legible handwriting.
"Hello, Guinea Pig-chan~" She greeted him cheerfully, hopping down from the chair the moment she noticed him and immediately shoving a potion tube toward his face. Inside sloshed a viscous, unsettling pink liquid.
"Drink this for me."
Tsutsumi stared at it for a moment.
"…Is it safe?" he asked, taking the tube anyway and holding it up to the light.
"Of course it's safe." Tachyon said it with absolute confidence, already pulling out a clipboard and pen. "This is the improved version of my best-selling potion. Since it's improved, it still needs testing."
Her pen hovered eagerly over the paper.
"Go on, drink it, my Guinea Pig."
Tsutsumi looked at her for a second longer, then shrugged internally and downed the potion in one go.
"Ugh-"
The empty tube slipped from his fingers and shattered against the floor as heat surged through his body all at once. His eyelid twitched, jaw tightening as he steadied himself.
Tachyon didn't even look up.
"This is Love Potion Version 4.5b," she said, scribbling rapidly. "I managed to triple the effect at the cost of duration. It should wear off once you manage to release yourself by jumping a trainer you li-"
She didn't get to finish.
Her back suddenly hit the table, knocking over several bottles and sending glass clinking across the floor.
"What the!? Wait, what are y-" She froze. "…Wait a minute. You're a male Um-"
Whatever she was about to say vanished when her lips was seal shut by his.
She struggles, her face turning crimson, body stiffening, her right fist pounding into his back, her left hand held onto his right hand, which was holding her head. Their body pressed against each other, so close that she could feel him pressing down on her, with the only barrier being the tight fabric of their clothes.
Tachyon's struggle only grew weaker, her mind becoming a hazy mess as the effect of her potion spread onto her, causing her to subconsciously lower her resistance and even kiss him back.
Her previously struggling hands moved to cling to him, her fingers clung onto the metallic fabric of his shirt as she slowly pulled it down, revealing his collarbone and chest.
Final Kamen Ride: Build Genius!
Instantly, his black clothes shifted to white, with many colorful bottles stuck onto the side of his head, shoulders, gauntlet, legs, and back. The Full Build Reactor on his chest glowed to directly neutralize the effect caused by Tachyon's potion for both of them.
They separated just as fast.
Both took a step back, breathing unevenly. The heat faded, replaced by the awkward silence of broken glass and overturned equipment.
Once both of them managed to calm down enough, Tachyon looked at Tsutsumi with interest, confusion, and lingering fluster all tangled together.
Tsutsumi, meanwhile, looked like he'd just endured a particularly annoying inconvenience.
"…Fascinating," Tachyon muttered after a moment. "The first ever male Uma."
She leaned in slightly. "Hey, can you strip so I can get a better look at your body?"
"No." His answer was immediate and flat.
The two of them nearly crossed the line just a few moments ago; if he hadn't reacted fast enough and if it wasn't for their clothes, he might have claimed her first blood just now.
Tachyon pouted for half a second before straightening up again.
"Aw, don't be like that, Guinea Pig-kun. I swear it'll be strictly professional research. I won't jump you."
She sounded confident, even placing her hand on her chest, looking all proud by it.
"With potions like that, you should be more worried that I would be the one to jump you instead." He replied dryly.
She leaned closer anyway, completely disregarding personal space. "C'mon. You don't want your secret exposed to the whole school, right?"
Tsutsumi met her gaze without blinking.
"If I can't remove the problem," he said calmly, "I'll remove the person causing the problem."
He raised his right hand and slowly clenched his fist. A few quiet popping sounds followed.
"Hey, hey! Let's not jump straight to violence!" Tachyon backed up quickly, hands raised as Tsutsumi stood and began approaching her at an unhurried pace.
...
The next morning, an Uma Musume with long, jet-black hair, a single white ahoge, and calm golden eyes stood outside Agnes Tachyon's dorm room.
She knocked lightly on the door with a soft fist.
"Tachyon, get up," She said in an even tone. "You're going to be late for classes."
Manhattan Cafe had done this often enough that it was basically routine. As Tachyon's friend, she knew exactly how her mindset worked. Once Agnes Tachyon got absorbed in something, basic survival necessities like eating, sleeping, or attending school became optional at best.
If Cafe or someone didn't show up regularly to check on her and bring rations, Tachyon might have starved to death at some point.
There was no response. Cafe waited a few seconds, knocked again, then sighed quietly. Reaching into her pocket, she pulled out the spare key Tachyon had given her "just in case I pass out again" and opened the door.
The room was empty. Cafe blinked.
The bed was untouched. The lights were off. No glassware bubbling ominously. No half-finished experiments threatening to explode.
That alone was unsettling.
She closed the door and headed toward the school lab, thinking Tachyon might have snuck in like last time.
She wasn't there either.
Which, admittedly, made sense. Tachyon had been officially banned from the lab after Tazuna found out she'd been selling love potions, stamina potions, and truth serums to other Uma Musumes.
The aftermath had been… noticeable.
Several male trainers had gone missing for short periods of time, only to be found later completely drained, severely dehydrated, and with shattered pelvises. Investigations were launched. And Tachyon got her lab privileges revoked.
So she had moved her entire operation into her dorm room instead, sacrificing both her own space and most of her roommate's to make room for workstations, ingredient storage, pill racks, and whatever else she was currently experimenting on. Her roommate didn't seem to mind, fortunately or unfortunately.
That still didn't stop her from occasionally sneaking into the lab anyway, right up until Tazuna personally showed up to kick her out.
Cafe paused in the hallway. This was starting to feel wrong.
After asking around, she finally got an answer that made her stop walking altogether.
Agnes Tachyon had found a trainer. And not only that, she was currently training out on the field.
Cafe stared for a few seconds longer than necessary.
With Tachyon's reputation as Tracen's resident Mad Scientist, most trainers, rookies and veterans alike actively avoided her. Very few teams were willing to take her in, no matter how talented she was.
Uma Musumes only had a three-year window before physical decline set in. Tachyon hadn't hit her prime yet, but she was getting close. If she didn't start proper training soon, even her peak might not be enough to compete with others in her generation.
The fact that a trainer had voluntarily accepted her was enough to send rumors spreading through the school.
Cafe immediately went looking.
After some searching, she finally found them.
Agnes Tachyon was running on a treadmill set up outdoors, her stride steady but intense. A massive gas tank stood nearby, connected to a thick tube leading into a gas mask strapped tightly to her face.
Standing beside her was someone Cafe didn't recognize.
An Uma Musume with purple and magenta tones, short hair with long side bangs. They wore a casual white hoodie under a beige trench coat, blue jeans, and mismatched red and blue shoes.
Tsutsumi watched Tachyon run without comment.
Sweat poured down her face, soaking her clothes, her breathing growing heavier as she continued inhaling the nebula gas. Yellow particles began to flicker faintly around her body.
Tsutsumi moved instantly.
"Pause."
He shut off the gas tank, and Tachyon quickly slowed the treadmill, pulling the mask away as she stumbled slightly, gasping for air.
"Here, rest. Then continue," he said calmly, handing her a water bottle.
Tachyon took it without argument, downed half of it, then poured the rest over her face before sitting down on the treadmill, chest heaving.
"…What's my level?" she asked between breaths.
Tsutsumi placed his palm lightly on top of her head.
"Hazard Level: 1.3."
Cafe's eyes narrowed slightly, not understanding what that meant but she decide to ignore it for now and return to class.
Agnes Tachyon was a scientist, a Mad Scientist, but still a scientist. And Tsutsumi, who got bored and decided to beat her at her own game, using her as his little Guinea Pig.
Last night, after pushing her to a corner, he made Tachyon spill to him her reason for becoming a scientist. She reveals that she pursued the limits of speed through science. The problem was that no matter how advanced her research became, it was still bound by the physical limits of an Uma Musume's body.
So Tsutsumi had shown her something else.
Build: RabbitTank.
He had casually jumped higher than Tracen's light poles. Then, just as casually, demonstrated that he could finish a hundred meters in under a second.
Agnes Tachyon had been hooked instantly.
And when Tsutsumi "accidentally" let it slip that she could use this power too, it was over.
Then, this Devil's Scientist has directly pumping her full of Nebula Gas, pushing her dangerously close to becoming a Smash before neutralizing the effects with Genius, then doing it again until she builds up resistance and does not become a Smash.
Last night, Agnes Tachyon had been screaming that she didn't want this anymore.
This morning, Tsutsumi suddenly pulled out a legitimate trainer license, dragged her out of bed, and informed her that training had started.