Susumu and Yui's only son, Katsuhiko, needs a huge amount of money to undergo surgery. A wealthy man named Sonoda says he will cover the entire cost of Katsuhiko's surgery under certain conditions, so Susumu and Yui go to see him in person as a last resort. Sonoda presents them with an outrageous condition: "I want to hire Yui as a sex slave for one year." Susumu is strongly opposed, but he gives in to Yui's strong desire to help Katsuhiko and signs the slave contract.