His eldest brother Kentaro Yamamoto, trusted by his younger brother, is steady and reliable. He has a temperament and is always brighter than his mind. He is full of longing for the underworld life and longing for the underworld. Kazuya Sugihara is an iron triangle in the underworld. , But because he did something wrong in an accident, he was about to be punished by the boss Inu Jin. Team leader Inukin gave them two choices, one is to apologize for death, and the other is to be sent to Thailand to undergo sex reassignment surgery, and then debut as an idol group. In the end, the three chose the latter, and in this way, the idol group Backstreet Girl with Ai Li, Jin and Qian Jia as its core members was born.