He plays percussion and is the leader of Blast, usually handling the business partnerships and financial decisions needed for the band's success. His favorite cigarette brand is "Black Stones", from which the band got their name. He is also a lawyer in training, despite his "scary" appearance (clean shaven head, many earrings and dark glasses). He's the big brother figure for Nana O—and sometimes Nobu—and acted as Nana's "guardian" when she arrived in Tokyo. While he harbors some feelings for her, he baits Ren to rekindle their love for each other. In the past, he shared several ties with Trapnest's members. Yasu and Ren grew up in the same orphanage and remained close friends when Yasu was adopted. He dated Reira while in high school and was jealous of Takumi's success and influence on her, which he later relates as the reasons for their break up. Also, he's the oldest member of Blast which Nobu sometimes teases him about (by calling him "old man"). He is in a budding romance with Miu to the surprise of Ren and others—who were sure he would date Reira again.
He is also in love with Nana.