Yazaki is Yuuka's husband or boyfriend in the OAV "Zero Sum Game." His brother, Keith, is the lead singer of the band "Zero Sum." Using his connection to Keith, Yazaki arranged backstage passes for himself and Yuuka to attend a concert. However, during the backstage visit, all band members except Keith kidnapped and raped Yuuka on the rooftop. Keith orchestrated this assault due to his obsessive feelings toward Yazaki. Following the assault, Yuuka suffers lasting psychological trauma, unable to forget or move past the experience. Yazaki's role centers on his relationships with Yuuka and Keith, with his actions initiating the events leading to the assault.