The deep sea is home to some of the most fantastic creatures the world has ever seen. And 200 meters below Tokyo Bay at the Magmell Deep Sea Aquarium, they're on display for all to see—Koutarou's idea of heaven. He's a shy boy, but Koutarou loves sea creatures and just landed a part-time job cleaning the aquarium. Follow Koutarou, his new boss, and all their deep-sea friends as a heartwarming coming-of-age story unfolds.