I didn't expect to be the first comment, this is a rather popular manga.
Anyway, yeah, if you are willing to take that level of revenge you are indeed a good candidate for hosting evil inside you.
I would normally either insult them and punch away until they knock me out or go to an authority if I'm level-headed enough at the time. Though that may not work for this guy in this story, as I've seen many stories where the authorities of the school don't really care about the children, or they purposefully give favoritism to one children over another, for example, the children of a whealthy man or a famous lawyer.
Life improsonment still seems a bit too high a punishment for being a teen bully.
I mean.. It's Japan. Who TF knows? Generally though people who assault others to this extent are going to grow up and be horrible people. He's not stealing food from him, or calling him mean names. He's not pissing on his gym clothes or stealing his book bag.
The Western concept of "bullying" and "harassment" have been watered down to the point that it encompasses everything. This isn't bullying. This is assault and battery. If you are an adult and this occurs to you, Police or self defense laws come into play.
This type of behavior speaks to a lack of socialization and empathy. He's already at the head of the totem in school, likely to be on top in society as an athlete. He's the exact type of person in the exact position that will escalate his crimes until there are too many victims to hide.
Also don't forget that the LARGE majority of violent criminals are repeat offenders.
I don't know how accurate it is in Japan for authority figures to look the other way on this type of behavior but I'm guessing it's vastly exaggerated. They have laws for corporate behavior and harassment so I don't see how they wouldn't have them for schools. Add to that the fact that this dudes family would be required to pay his victims medical bills and compensation..
With very little effort in the modern day you can collect evidence.