He was betrayed by the Sheep group.

Shirase stabbed Chuuya in the stomach with a knife soaked in rat poison.At the same time,other members of group gathered,people who opened fire on him.He fell down the cliff next to the sea.You couldn't phone him for a long time,so you went to search the area where he usually works.When you surveyed the area,you came to that cliff and saw him.He was sitting with his back against a rock,trying to do something with a knife.