Reika Aoshima serves as the de facto leader and a core member of the East Oizumi Academy cosplay club. She maintains a serious, disciplined, and sometimes stubborn demeanor, often appearing stern or unfriendly compared to her fellow club members. This attitude arises from her intense focus on their shared objective: competing in and winning the Cosplay World Series. Her frustration stems from the club's frequent lack of concentration and disorganization.

She possesses silver hair and wears glasses, a fact known solely to Gorō Yorozuyo, the club's president and its only male member. Gorō harbors significant romantic feelings for her, which frequently result in awkward interactions, especially when he reads erotic stories aloud in her presence.

In her leadership role, Reika manages the club's activities and logistics. This includes reluctantly approving fundraising competitions despite her concerns over financial stability. During a critical cosplay battle against the rival Shin-Takarazuka Academy club, she is cornered and molested by their leader, Ranko Takara, in a storage room while Gorō provides dramatic narration of the event.

Reika's unwavering dedication to the club's success and her position as the primary disciplinarian shape her interactions, contrasting sharply with the more carefree attitudes of the other members.