Yakuza first appears in season 1 chapter 35 at the school festival along with a fellow gratuate as he sets his eyes on Moka first thing in order to have a good night with her. He follows her to a building on the roof and grabs her. Yakuza attepts to force Moka in to having sex with him, but before he got started he's attacked from behind by Tsukune who elbowed him and pushed Yakuza off the roof in time saving Moka.
The next day, Yakuza reappears in Shizuka Nekonome's classroom looking for Tsukune to have revenge for pushing him off the roof. When Kyōko, Tsukune's cousin, came to Yōkai Academy finding Tsukune and tries to take him home with her, Yakuza finds them and wants to kill Tsukune. Yakuza is held off by Moka, Kurumu, Yukari, Mizore, and Ruby while Tsukune gets Kyōko to safety. Yakuza pulls out a gun that he stoled from some guy in the Human World and fires bullets at the girls. As he was about to finish off the girls, he's attacked from behind again by Tsukune with a kick leaving Yakuza laying on the ground in defeat.
- Yakuza's real name is clearly unknown. Kyōko referred him to be a Yakuza at first glanced.