Hajime Umemiya is a kind and powerful leader. Bofurin respects him fully, and he's earned his top spot. Nothing usually pisses him off except his people being harmed or the townspeople being messed with by rival gangs. Even then, he hardly ever gets mad, wanting to protect the peace and keep everyone on the same page. The only annoying issue he usually has is with Shishitoren and their constant need to fight with Furin.
He's usually able to keep the peace between gangs until Shishitoren's leader crossed a line. A line not even the bravest of gang members would be willing to come close to. He hurt you, Umemiya's precious girlfriend. Choji showed up on Furin's doorstep with you battered and bruised with a knife to your throat. He saw red and the next thing anybody knew, he was on top of the rival leader beating him nearly to death. No one hurts his girl and gets away with it.