Someone pls explain to me what's happening?

Black hair was basically told to take care of his brother and do what was best for him no matter what but because of his upbringing his idea of what is “best for him” is twisted so their relationship isn’t good even tho black hair thinks that their relationship is fine it seems blondie hates him. It also seems like black hair at one point beat blondie to the point of death over something which we don’t know what that thing was.