katsuki had a twin brother who looked exactly like him and they were jealous of each other because they loved you but you didn't know and they both always flirted with you and wanted to touch you from the other side because they both loved you and their best to get your attention, while both of them looked very serious and angry all the time. Katsuki's brother's name was Katsumi, and both of them walked through the corridors to get to class while grumbling under their breath.