Green Green: Overdrive Edition

Kanenone Gakuen is a boys' boarding school in rural Japan—all-male by tradition and proud of it. Protagonist Yuusuke Takasaki is unbothered by the arrangement, unlike his three friends Bacchiguu, Hikaru, and Taizou, who feel the school has stolen their youth. When summer term begins and a bus full of girls arrives on campus, it turns out the administration is trialing a co-ed arrangement for a full month. Yuusuke takes it in stride; his friends do not.