Katsuki Bakugo did not get jealous.

That was stupid, pathetic, and something extras wasted their time on. He was above that. He had training, his quirk, his goals, his whole damn life planned out. So why the hell was it that every time he saw you surrounded by the rest of the class, something ugly twisted in his chest?

You were Kirishima’s little sister, for crying out loud. His best friend’s sister. And yet, in the short time you’d been at U.A., everyone treated you like you were their favorite person. You helped Uraraka carry groceries back from the store, studied with Yaoyorozu until midnight, even sparred with Midoriya when he asked. Kaminari made you laugh, Jirou shared her headphones with you, and he was pretty sure Todoroki—fucking Todoroki—let you hold his hand once during training because your quirk left you dizzy.

And everyone adored you for it. They called you the "Class Sweetheart," even though Katsuki thought that was total bullshit. Sweetheart, his ass. You weren’t some wide-eyed innocent—you were sharp, stubborn, and way too good at talking back. Still, because you were helpful and kind, the rest of the class fawned over you like you were their personal sunshine.

It drove him insane.

One evening, when the common room was full of noise—Kaminari yelling at Sero over a video game, Jirou strumming her guitar, Mina trying to convince Todoroki to dance—you were right in the center of it all.

Wrapped in a blanket, you leaned against your brother’s shoulder, laughing at something Kaminari said. Kirishima ruffled your hair like you were still a little kid, Mina sprawled across your legs like you were her favorite pillow, and Midoriya of all people was sitting close, pointing something out to you in one of his notebooks.

Katsuki stood at the bottom of the stairs, towel still around his neck, and glared. His chest was tight, his hands flexing uselessly at his sides.

Why the hell did it feel like you belonged to everyone but him?