Returning home to his parents' house, Koji sensed tension in his older brother's strained marriage. After talking, he learned that his sister-in-law, Jun, desperately wanted to get pregnant and had been having sex with her husband every night. Koji intended to stay out of it, but accidentally stumbled upon them in the act. Jun, realizing he was watching, continued exposing her lewd behavior, staring at Koji with a disturbing, provocative gaze. Desperate to conceive, she pressured him to donate his sperm, insisting that as siblings-in-law, it would be acceptable. Overcome by her relentless, sweaty advances, Koji could no longer resist and erupted deep inside her vagina.