Kasumi Shiina is a friendly and kind-hearted high school student, though occasionally clumsy in her actions. Despite these traits, she remains popular among her peers. She possesses distinctive pink hair and red eyes, standing 1.58 meters tall with measurements of 84-56-83.

She shares a deep platonic bond with fellow student Kensuke, stemming from a past event he no longer recalls. This history fuels her hesitation to confess her genuine romantic feelings for him. When struggling emotionally over this conflict, she retreats to the solitude of a church confessional to privately gather her thoughts.

Kasumi becomes a member of the covert school group, the "Love Club," which operates from the basement of the school church. This organization studies romantic behaviors and assists students with love-related issues, directly defying the school's ban on such activities. Her involvement coincides with Kensuke joining the club, but her initial romantic focus appears directed elsewhere, complicating their dynamic.

The club engages in practical training for dating, romantic expressions, and sexual experiences, framed as educational projects by its female members. Within this setting, Kasumi's role connects to broader explorations of romance and intimacy.