1. I don't think the MC thinks of himself as "on the side of justice". It's revenge, only mitigated by the possibility of forgiving a redeemed target. He's otherwise a good kid who got handed a bad situation. (Being targeted by the worst kind of bullies ever.)
2. "Real justice", not sure what he means by that. I hope it doesn't stop at "law enforcement", because that's only one aspect of justice. BTW, where is "justice" in regards to people who killed two adults, seriously maimed a kid, all to try and push yet another kid to suicide? "Revenge" is certainly not "justice", but neither is a police force and a set of laws who can't do anything against criminals. Mr Cop will have a lot to do in order to show us "real justice". I do have some hope in this guy though. He doesn't seem the sort to just pretend that applying the letter of the law is "real justice".