A sports club at the high school attended by all high-school aged characters in the show, it is notable for including every single high-school age character except Haruka, who refuses to join because she needs to take care of her sisters. Because of Haruka's skill at the sport, this displeases Hayami, who plots various ways to get her to join, including telling Hosaka to try and recruit her. The club is probably intermural, but they are never shown in competition.
Hayami and Hosaka captain the female and male teams, respectively. Maki and Atsuko are also participants. That Hitomi's participation is likely is deduced from a scene where, when Hitomi seeks out Maki, Maki asks if she is here to ask about club business. It is, however, not certain. Natsuki seems to be a rare attendant, like Haruka needing to take care of his siblings.