54 – Equations
Ochaco had asked me to come to the study session and I'd said yes because she'd asked me in the hallway with her hand on my sleeve and her brown eyes doing that thing where she tilted her head and looked up and I was physically incapable of saying no to that angle.
So I was sitting in the 1-A study room at four in the afternoon watching Momo Yaoyorozu explain organic chemistry to eight students who needed it and two who didn't.
The study room was on the third floor, past the library, with a long table and a whiteboard that Momo had already covered in molecular diagrams. She'd brought her own markers because the school-issued ones were "imprecise in their line width." She was standing at the board in her school uniform, her hair in the spiked side-ponytail, her sleeves pushed up to her elbows, and she was drawing a benzene ring with the confidence of someone who had memorized every atom in the room and could rebuild the whiteboard from lipids if someone broke it.
Ochaco was across the table, taking notes in a notebook with a price sticker still on the cover. Kaminari was next to her, copying Ochaco's notes because he'd given up following the board. Jiro was next to Kaminari, one earphone jack plugged into the desk, probably listening to music while pretending to study. Sero was doodling tape patterns in the margins of his handout. Kirishima was genuinely trying and his forehead was creased with effort that would've been more productive in a gym.
Momo was explaining electrophilic aromatic substitution. Her voice shifted when she was teaching. Still formal, still polished, but faster, more fluid, her sentences running into each other when the concept excited her. She'd gesture at the board and her hand would trail the molecular structure like she was drawing it in the air from memory, which she was, because the board diagram was just a visual aid for everyone else. She already had the whole thing in her head.
"The electrophile attacks the pi system here," she said, tapping the board. "The carbocation intermediate is stabilized by the adjacent electron-donating group, which is why the substitution occurs preferentially at the ortho and para positions rather than meta."
She drew an arrow. Clean. Precise. The line width was, as promised, exact.
"But if we consider the resonance contribution from the nitrogen lone pair," I said, "the electron density at the para position is actually higher than at ortho because of steric effects from the methyl group. The selectivity isn't just electronic. It's spatial."
The room was quiet.
Momo's marker stopped on the board. Her hand was still raised, the tip a millimeter from the surface. She turned her head and looked at me.
"That's..." She paused. Her eyes moved from me to the board and back. "That's a correct analysis. But that interaction between steric and electronic factors isn't in the U.A. curriculum. It's typically covered in university-level organic chemistry."
"I read ahead."
"In university textbooks?"
"I like chemistry."
She held my gaze for a second. Two. Her onyx eyes were sharp and steady and her mouth was a flat line of assessment. Then she turned back to the board and drew the methyl group steric interaction I'd described.
"Hayami-kun is correct. The selectivity at the para position is enhanced by steric hindrance at the ortho position. This is an advanced concept, but it demonstrates why empirical observation should always supplement theoretical prediction."
She kept teaching. The session went on. Kaminari asked what "electrophilic" meant for the third time and Jiro unplugged her jack long enough to say "it likes electrons, Kaminari, it's in the name." Sero finished his tape doodle. Kirishima asked a genuinely good question about reaction rates and Momo's face lit up and she spent four minutes on an answer that was twice as detailed as the question needed.
I sat there and replayed the last two minutes in my head. The steric-electronic interaction was first-year organic chemistry. In my real life. In my previous life. Where I'd taken organic chemistry in a university that didn't exist in this world, in a country that didn't have Quirks, as a person who wasn't Ryo Hayami.
I'd corrected a girl whose Quirk required her to memorize atomic structures for a living with knowledge from a life she couldn't know about.
Stupid. I'd been so focused on the actual chemistry that I'd forgotten where the knowledge came from. The body's memories included high school education. The body had never taken university organic chemistry. Ryo Hayami, orphan, hero student, registered Quirk "Enhance," had no reason to know about steric effects on electrophilic substitution.
The session ended at five. Momo erased the board, organized the handouts, and thanked everyone for coming. Ochaco walked past me and bumped her hip against my shoulder as she passed, a small private contact that nobody else saw. Kaminari was asking Jiro if she wanted to get ramen and she was saying "only if you're paying" and he was saying "I was hoping you'd pay" and they walked out arguing about it.
I gathered my notes. Momo was at the whiteboard cleaning the last marker residue with a cloth she'd Created from her palm. The fabric appeared in a brief shimmer of light from the exposed skin on her wrist, fully formed, purpose-built. She wiped the board and the cloth dissolved back into particles when she released her focus.
I headed for the door.
"Hayami-kun."
I stopped.
Momo was standing by the whiteboard. The cloth was gone. Her hands were at her sides.
"Can I speak with you for a moment?"
The hallway outside the study room was empty. Late afternoon light came through the windows at the end of the corridor. The cleaning crew had already passed. The floor was damp and smelled like lemon. Our footsteps echoed.
She walked next to me. Didn't speak immediately. Her hands were clasped in front of her, fingers interlaced, her posture straight, like someone who'd grown up with tutors who corrected her spine.
"You know things you shouldn't," she said.
I kept walking. My feet on the damp tile. The lemon smell. The windows throwing long rectangles of light across the floor.
"During the Battle Trial in our first week," she continued, "you told me that Kaminari would short-circuit if he exceeded his output threshold. That was our first joint exercise. You'd never seen him use his Quirk at full power. But you knew the failure mode."
"He talked about it in class."
"He didn't. I checked." She said it without emphasis. A correction, delivered flat. "Kaminari's short-circuit isn't public knowledge within the class at that point. Aizawa's file might reference it. Students would have no access to that file."
I didn't answer. We walked past the library. A third-year was visible through the glass doors, asleep on a stack of textbooks.
"At the Sports Festival," she said, "you told Midoriya that Todoroki wouldn't use his fire. You said it like a fact. Todoroki hadn't used his fire in any public exercise at U.A. You shouldn't have known he had fire at all. His registration lists only ice."
"His dad is Endeavor. It wasn't hard to figure out."
"The inference is reasonable. The certainty wasn't." She looked at me. "You didn't say 'he probably won't use fire.' You said 'he won't.' You were right. But the confidence required information, not deduction."
We reached the end of the corridor. The stairwell. She stopped walking. I stopped. The rectangle of window light was between us, a bright stripe across the floor.
"You give tactical advice that assumes knowledge of people's Quirk limitations before you've observed them," she said. "You knew Kirishima's Hardening had a duration limit. You knew Tokoyami's Dark Shadow was weaker in bright light. You knew the timing of Aoyama's laser before he'd used it in front of the class." She paused. "And now you're correcting university-level organic chemistry that you shouldn't have studied."
She wasn't angry. Her voice hadn't changed in pitch or volume. Her hands were still clasped. Her eyes were steady. This was Momo the analyst. The girl who could build a matryoshka doll from memory because she'd catalogued every layer of painted wood. She'd been cataloguing me the same way. Every slip, every too-accurate prediction, every piece of knowledge that didn't fit the file on Ryo Hayami, Seat 19, Quirk: Enhance.
She'd been building a dataset. And the dataset had enough points to draw a line.
"I pay attention," I said.
"I pay attention too." She stepped closer. Close enough that the lemon floor cleaner was replaced by something lighter. Her shampoo, or her soap, whatever it was. Clean and faintly floral. "And the attention doesn't explain the scope of what you know. Attention explains noticing. It doesn't explain predicting."
The word sat between us.
"Are you asking me if I can see the future, Yaoyorozu?"
She blinked. The composed mask cracked for half a second. Her eyebrows went up, her lips parted, genuine surprise that I'd said the quiet part that loud. Then she laughed. Short, startled, the sound escaping before she could modulate it. Her hand came up and covered her mouth, the formal gesture of someone who'd been taught that laughing openly was impolite.
"No." She lowered her hand. "That would be absurd."
"It would be."
She looked at me. The laugh was gone. Her eyes were dark and steady and her mouth was a line and her head was tilted at the angle of someone running calculations she hadn't finished.
"But you know things, Hayami-kun. You know things that attention and intelligence don't explain. And I'm very good at recognizing when an equation doesn't balance."
She straightened. Smoothed the front of her blazer. Adjusted the cuff of her left sleeve.
"Thank you for the study session," she said. Formal again. "Your chemistry insight was genuinely helpful."
She turned and walked toward the east stairwell. Her ponytail swayed. Her footsteps were even on the damp tile.
I stood in the hallway. The window light was moving. The third-year in the library had woken up and was staring at his textbook with the expression of a man who had forgotten what reading was.
Momo Yaoyorozu had been watching me since the first week. She'd catalogued every moment where I knew too much, reacted too accurately, predicted too confidently. She didn't have the answer. Transmigration wasn't in her vocabulary. But she had the pattern.
I needed to be more careful. I'd been coasting on the assumption that foreknowledge slips were small enough to dismiss. They weren't. One person had been watching the whole time, and she was the smartest person in the building.
The hallway was empty. The lemon smell was fading. The window light had shifted.
I pulled out my phone. One text from Mina: a picture of a cat she'd seen on the way home, orange, missing half an ear. "YOUR CAT" with three exclamation marks.
I typed back: "that's not my cat."
Three dots. Then: "he LIVES by your building. he's YOUR cat."
I put the phone away and walked toward the exit. The sun was lower. The campus was clearing out. A second-year was practicing a Quirk in the courtyard that made his forearms glow, and a teacher I didn't recognize was telling him to stop doing it near the windows.