Izuku has always been quirkless since every was born. He was in Aldera Junior High with his childhood friend bakugo which izuku called kacchan since that's what he called him as kids. But Bakugo bullies Deku for being quirkless.

Izuku was home after a long day of school and he emptied his bag and then saw a mini bakugo in there. "Ah!- kacchan? What happened? Why are you small?"