Three months have elapsed since Iori Kitahara started residing above Grand Blue, his uncle's scuba shop, and enrolled in the university"s Diving Club. Together with the other members, he has spent his days drinking and indulging in reckless fun. When his sister Shiori learns of his antics, she resolves to intervene and bring him back home to take over their family inn. Despite her best efforts, Shiori temporarily relents after seeing how Iori has become attached to Grand Blue and his friends. While Iori and the rest of the Diving Club continue partying like there is no tomorrow, they find themselves in bizarrely amusing situations yet still manage to sharpen their scuba skills. Their adventures keep growing, blending friendship with underwater training everywhere they dive.
