revenge for what????

for destroying his dream emo squad lol

WHAT DREAMMM??????? LMAO

I think it probably has something to do with the lady in the flashback. I'm assuming it's his mom and something tragic happened to her (and it was through her death that he got the human sacrifice to get his powers ;;; ) :'c

Yeah. I don't know how that wasn't understood by the others, though.

IM SORRY IM DUMB ASF

It wasn't explicitly stated though to be fair. The mangaka seems to be setting it up for a big reveal later on I guess xD;