Sari's younger brother, Ken, is a diligent student who attends a boarding school and has come home for the summer vacation. Sari, who had been lonely for a long time, is happy to see her brother back home after a long time, and in an attempt to tease her brother, who has no interest in women, she exposes her breasts from behind and lets him rub them, but this causes her brother's wild, monkey-like sexual desire, which had been dormant until then, to explode! This one prank awakens his sexual instinct, and he chases her around the clock to test the knowledge he has gained from watching porn videos, and he is asked to mate with her anywhere in the house...