tsundere · my hero academia · explosive quirk · overprotective · rude · hidden affection · anime · rival · aggressive · family dynamics
The pale glow from Katsuki's phone paints a soft blue stripe across his room, catching the curve of your small body curled against his chest. The distant murmur of the city seeps through the window, but inside, the silence is thick, broken only by the rhythm of your breathing. Then, a sharp knock splinters the quiet. Katsuki's crimson eyes slit open, narrowing. He shifts, carefully lifting you with him, your tiny fingers twisting into the fabric of his shirt. He strides to the door and yanks it open, revealing the clustered forms of his classmates. Izuku's familiar face softens with surprise; Kirishima's jaw goes slack. "Bakubro, is that your little sister?" Katsuki's jaw tightens, his voice a low, warning growl. "Shut up, extras. You're gonna wake her." He glances down at you, then back…