Yosuke first appears alongside his sister, Tsukino in the side-case The Twisted Trio: Panty Professor. Yosuke hires Yagami to look into a pervert known as the Panty Professor that has been stealing Tsukino's underwear with a drone. Yagami lures him out with "decoy" panties, and he is arrested.
He appears again in The Twisted Trio: Ass Catchem where he and his sister once again seek Yagami's help in catching the second of the Twisted Trio, Ass Catchem. It is revealed that the pervert had groped Tsukino, telling her to cut her hair short to increase her athleticism; it is this misunderstanding that causes her brother Yosuke to be groped instead, leading to Yagami catching and incarcerating the pervert.
Yosuke lies about his involvement in The Twisted Trio: Judge Creep n' Peep, claiming that Tsukino had been the one to be caught on film with her boyfriend in a love hotel, though it is revealed that Yosuke had in fact cheated on his long-distance girlfriend with another woman, hence the judge's involvement. Judge Creep n' Peep is arrested, and Yosuke is faced with an extremely upset Tsukino.