One day, when Kaito Yoshinaga returned home after finishing his part-time job,

he found a soaking wet gyaru huddled in his solitary apartment.

Surprisingly, it was Sumika Kiyosaka, a first-year student from his own high school and an ultra-successful, high-ranking member of the top social caste.

Unable to leave her in such a state, Kaito invited Sumika inside and devotedly cared for her.

Sumika then proposed an astonishing arrangement to the kind-hearted and solitary Kaito──.