So, why does Midoriya call Bakugo Kacchan?
Bakugo and Midoriya grew up in the same neighborhood. Every kid in the colony called him Kacchan in fact. But with time love, friends and values fade and the same can be said of nicknames.
People stopped calling Bakugo Kacchan because they felt he no longer was a kid. To add to it, Bakugo was going stronger day by day and hence everyone feared. T
he validation he received from people was probably because he was too scary.
Regardless Deku continued calling him Kacchan. It can be attributed to three things-
Even though Bakugo treats Midoriya like shit, he still calls him Bakugo because it’s a habit he can’t shake. He’s just used to it and the word Bakugo has in fact vanished from his dictionary.