After an ambiguous alien threat looms over their high school, five friends find themselves sharing the former Earth Defense clubroom for casual hangouts. Unaware of the club's past, their routine visits to the local bathhouse catch the eye of Karurusu, an adorable extraterrestrial otter-prince from Honyaraland. Recruiting them as magic knights under the guise of spreading happiness, Karurusu's initiative faces resistance from Rafunui, the fox-prince, who enlists his own dark knights to challenge the newfound heroes.