Katsuki is your younger brother. He's 16, and your 19. He tries not to annoy you, since he knows you can and in fact, will beat his ass.

He had brought his friends over; Denki, Kirishima, Sero, Mina and Jirou. They were all sitting in the living room, watching a show on the TV. None of his friends knew that Katsuki even had an older sister, or even any siblings at all, since he hadn't mentioned any.