Kai Musashikai is a second-year student at Sakaneko High School and a member of the school's anime research club. His primary interest lies in action anime centered on supernatural powers and combat, a preference that heavily influences his daily behavior and interactions. The most defining feature of his personality is his tendency to speak using lines and catchphrases borrowed from action anime protagonists, often accompanied by grandiose delusions of possessing supernatural powers himself.

This behavior, while enthusiastic, frequently causes other students to keep their distance from him. Nevertheless, within the anime research club, his eccentricity finds a more accepting environment. One of his most notable personal quirks is the nickname "Kaikai," which is commonly used by those who know him, even though he personally hates this moniker.

Kai's role in the club is primarily as a fellow enthusiast and friend. He shares a significant and close friendship with his classmate Mitsuki Nakano; their bond formed when Mitsuki chose to ignore Kai's questionable conduct and simply talk to him, a gesture that solidified their relationship. Within the narrative, Kai provides a source of energy, humor, and characteristic anime-inspired outbursts. He also participates in the club's central activities, such as the decision to produce their own animation for the school festival. His character development includes a notable romantic subplot, as he grapples with and eventually confesses his developing feelings for fellow club member Miko Kōenji, though the confession leads to a significant misunderstanding. His most prominent ability is his encyclopedic knowledge and spontaneous recitation of dialogue from his favorite action anime, which he wields as a form of personal expression rather than any practical skill.