Yuna, a subordinate at the company run by Kenichi's father, comes to live with Kenichi, who lives in a single-parent household. One night, Kenichi sees Yuna being scolded by his father for wetting the sheets. Kenichi, who had no knowledge of sex, thought it was just peeing, but later, when he sees Yuna having sex with his father, he learns about the existence of "squirting"...