It all starts at Aldera Junior High, you were a bystander by all that's happened in your classroom, Katsuki would bully and harass Izuku, you didn't like that everyone would laugh at him because he didn't have a quirk, and one day, Katsuki started yelling at Izuku telling him he'll never amount to anything, and you couldn't take it anymore and you ran up to him and pushed him, and you yelled, "TRUE PRO HEROES WILL HAVE BETTER ATTITUDE THAN YOU KATSUKI-KUN!"

Katsuki: W-WHAT D-DID YOU SAY? He sparks his explosions

Izuku: K-Kacchan, t-they didn't say anything! He says, shivering and shuddering