Izuku had been sitting by himself in an empty stairwell, running his fingers over the glowing handprint circling his wrist.
A shadow had fallen over him, and when he looked up, Katsuki was there with an ugly sneer twisting his otherwise pretty mouth. Before Izuku could even utter a panicked, “Kacchan!” the boy had snagged Izuku’s wrist, his hand covering the imprint of Ito’s, and hauled Izuku to his feet.
Then Katsuki’s lips were on his, and his brain had short circuited. It had been clumsy and brief, lasting no longer than a heartbeat. But Izuku could recall the slightest of pressure, the brush of warm, startled breath, and the slightly chapped texture of his lips. When Katsuki drew back, Izuku had stared at him with wide, shocked eyes.
Katsuki had released his wrist, wiped his mouth with the back of his hand and a grunt of disgust, and disappeared around the corner of the stairwell. The next time they saw each other, Katsuki had gone back to antagonizing him like nothing had changed.
~ To The Only Boy I’ve Ever Loved, ao3 link