“And people criticize my taste in media,” Ryouma scoffed. “I’ve seen that one a couple of times. A genin could take down those kids. Maybe even an Academy student. Probably even my street-kids...”

Katsuko threw a blueberry at his forehead and hoisted herself up to turn on the TV anyway. Ryouma ate another spoonful of oatmeal and tilted his head back to study the seals taped to the ceiling. Kakashi’s fingers combed lightly through his hair. He sucked on his spoon, eyes drifting half-closed.

“Y’know,” he said dreamily, as Katsuko flipped through two variety shows and the cooking channel, “the third one from the left looks an awful lot like something I saw in Mist. I was there on a mission, years ago. On recall from Team Badass. There was this guy who could paint seals on things an’ they’d detonate, even without explosion tags.” He squinted a little more, letting the lines blur together. It was upside down and sideways, and there were more squiggles in the center than he remembered, but the basic structure still looked similar.

“I tried to learn how he did it, but he wasn’t too keen on sharing, an’ I’m not too good with seals. Would’ve been cool, though. You didn’t even have to feed your own chakra in for the explosion, beyond just a dribble for the ignition. Sort of fed on itself after that...”

Kakashi went very still beneath him. His chin tilted slightly, as if he was following Ryouma’s line of sight. “An exponential loop,” he murmured absently, “but I looked at that already...”

Every muscle went rigid. Ryouma tensed in reflexive sympathy, but Kakashi was still staring at the ceiling.

“Mist,” he breathed. “It’s not Aken Shaneo, it’s his student. That’s Kamiya Ukan’s energy work! That’s why it’s not making sense. It’s not conversion, it’s a chain reaction--Kunuya’s Law. That’s why the drain is self-sustaining!”

His bowl of oatmeal clattered untouched to the floor. Kakashi seized Ryouma’s head in both hands, bent double, and kissed his forehead. “You’re a genius.”

Then he was scrambling up to grab the nearest set of scrolls and riffling through them so savagely that a few almost tore. He sprang onto the desk, yanked the seal-sketch down from the ceiling, dropped to the floor again, and went on another mad search for pen and paper in the organized chaos of his desk.

Ryouma rolled slowly to his stomach. Katsuko was watching Kakashi, too, wide-eyed, lips parted. On the TV, a perky young woman told her how she could preserve fresh vegetables longer with a green plastic bag. Katsuko ignored her. But her lips pressed tight together, and the blooming hope in her eyes faded. Her face shuttered. She stood suddenly, stiff, almost jerky. “Excuse me.”

Kakashi didn’t hear her.

Ryouma sat up, but Katsuko shook her head and slipped past him into the bathroom. The door closed quietly behind her, and Kakashi reached for another book.