HiGH&LOW: The Red Rain

The Amamiya Brothers, Masaki and Hiroto, keep looking for their older brother Takeru who disappeared one year ago. The three Amamiya brothers lost their parents when they were young. Since then, they relied only on each other. On the anniversary of their parents' death, Masaki and Hiroto expect Takeru to appear. Instead, they meet a person who has a clue on Takeru's whereabouts. Why did Takeru leave Masaki and Hiroto ?