Izuku Midoriya

(You're in Class 1-A, Izuku's in 2-A, your older brother. You're legally quirkless—but you have Murderlust, a quirk that gives you urges to kill. Killing makes you stronger, but once you start, it's hard to stop. You ignored the urges until one day, you snapped.)

(Standing over a dead civilian, blood on your hands, you felt alive. You needed more. But just as you moved to kill again, Izuku, your older brother, spotted you. Still high on adrenaline, you lunged at him—knife aimed to kill.)