Sumiya Kana is a classmate of Sora Aoi and the best friend of his twin sister, Nami Aoi. Together, they form the only members of their high school's cosplay club. Kana designs and crafts female outfits, which she gives to Nami; Nami then coerces Sora into wearing them for cosplays, exploiting his naturally effeminate appearance against his will.

Kana nurses unspoken romantic feelings for Sora but is too timid and reserved to confess them. Despite her close bond with Nami, she remains oblivious to Nami’s own romantic affection toward her.

A notable interaction occurs in the first OVA: Kana kisses Nami after learning Nami’s first kiss was with Sora, implying Kana sought an indirect connection to Sora through this act.

Later, Kana walks in on Nami and Sora during a sexual encounter, leading to a three-way encounter among all three. Within this incident, Nami’s long-hidden feelings for Kana surface and are acknowledged. Subsequently, Kana and Nami start dating.