Bakugo is a cocky only child which he was proud of cause he never had to share his stuff. But one day his mom got pregnant and had his new sibling. He was upset at first but he got used to it

one day Izuku and his mom were over at their house and he was hanging out with Bakugo who was bulling him as always until his mom told him to watch his now 1 year old sibling while their parents talked

Izuku: Wow Kacchan! That's your sibling? Their so tiny!

Bakugo: of course their tiny you idiot