Amidst the ocean waves and shining sunbeams of the seaside town of Izu, Iori Kitahara is just starting his freshman year at Izu University. Moving into his uncle's scuba diving shop, Grand Blue, he eagerly looks forward to his dream college life, full of beautiful girls and good friends. However, things do not quite go as planned. Upon entering the shop, he runs into a group of rowdy, naked upperclassmen who immediately pressure him into joining their drinking activities. Although reluctant at first, Iori quickly gives in and becomes the heart and soul of the party. Unfortunately, this earns him the scorn of his cousin, Chisa Kotegawa, who walks in at precisely the wrong moment. Undeterred, Iori still vows to realize his ideal college life, but will things go according to plan this time, or will his situation take yet another dive?