While returning to school during summer vacation to retrieve a notebook, a student accidentally discovers his classmate, Sukumi, masturbating in the changing room. Despite her harsh exterior and insults, the encounter sparks a secret, daily arrangement where the two explore their mutual lust through various fetishes and roleplay.
Yui and Sukumi explore their relationship through a playful maid-and-master roleplay, leading to intense intimacy. After Sukumi rejects the advances of others to remain loyal to Yui, the two share a romantic encounter wearing school swimsuits. They exchange their first kiss and pledge their everlasting love to one another, deepening their bond as their summer vacation continues.