I wonder how little Kai made those bully apologize. They looked scared, so it probably wasn't just, "Please stop bullying others."
It probably was more like, "If you don't stop bullying others, I'll tie you up with a chain, attach a bunch of concrete blocks to it and throw you off a bridge into the river."
It's nice that he is truly a good older brother. I also wonder how he go together with his now ex. They seem pretty different.