Iori Kitahara leaves Tokyo to begin university in a seaside town, where he moves in with his uncle, the owner of a diving shop called Grand Blue. Expecting a quiet new student life, he quickly discovers the local diving club, whose members are just as passionate about the ocean as they are about wildly chaotic parties. Between training sessions, competitions, friendships, and increasingly absurd situations, Iori gradually learns to appreciate scuba diving despite his initial reluctance. Alongside Chisa, Kohei, and the other members of the group, he discovers both the beauty of the underwater world and the joys and excesses of an utterly unpredictable university life.