In order to pay for Jun's hospital fees, Yukio and his friend Tetsu sneaked into the Seidokai to steal money. They were caught by Hyodo, though, who offered them the chance to leave unharmed in return for Yukio visiting the Seidokai office once a week.
When Yukio was younger, his mother, Tsubaki, had been raped by Ashiei and gave birth to Jun, but soon after became ill and passed away. Ashiei then taught Yukio how to become a prostitute so that he could earn money to take care of himself and Jun. Resentful of Ashiei, Yukio then set his body on fire in a failed attempt to kill him. This incident is also the origin of the scars on Yukio's back.