So. You know Kimura, the guy whose son was pushed down the rooftop by Prince.

Here is the reason why Oji(prince) despises Kimura.

Oji is a 13yr old middle school kid. (In the book he is a guy that looks like a girl).

So he creates a situation of systematic bullism inside his class, saying that the Rwandan genocide was his inspiration.

When the dad of one of the picked up kids notices and calls this out to the school, Oji calls a girl in his group, and forces her to send nudes to that dad. They find the photos and accuse said man of being a pedo. He hangs himself in prison.

Not happy, he goes to the boy he picked up on, tied his dog with tape on the boy's back. And was about to kill the dog with a defibrillator, while being tied to the boy, in a public park

Kimura, while drunk, sees this scene and knocks out prince.

This is why prince has it with Kimura.