Iori Kitahara moves to a diving shop named Grand Blue run by his uncle as he prepares to start his college life there. He lives under the same roof as his cousins, Nanaka Kotegawa and Chisa Kotegawa, who he has not met for a decade. Iori Kitahara looks forward to living a pleasant college life, but he ends up becoming the target of the college diving club. Even his best friend, Kohei Imamura, who is an anime fanatic, joins the diving club. Thereafter, Iori is swept up by the other members of the club, who spend more time drinking, partying, and stripping naked than actually diving.