Shuji returns from Tokyo to see his brother after so many years of absence. He never did get along with his Brother, to begin with. But he was forced by the turn of events in Tokyo.
In Tokyo, Shuji had an ongoing business but he was tricked by his business partner who ran away with the money. He then had no choice but to return to his brother to ask for money. Something that pisses him off, because he knows this brother despises him. He accumulates more anger from the fact that this Brother got married to the girl he had a crush on = Kana Yume.
The brother effectively took the life he was supposed to have.
The brothers have an argument and they are both furious. On this junction, Yume Kana is all sweet and kind… something that pisses Shuji even more. When his brother is gone to work Shuji finally bursts in an explosion of violence and rape.