The story starts with Tatsumi, a young man, returning to his home, where he is greeted by the merman Wakasa, who lives in his bathtub. The latter is given a bath mix, which would make it possible to turn the bath water pink, something the merman has always dreamed of. Meanwhile, Tatsumi reminisces about their first meeting and how he had taken him to his home, after he found the powerless merman stranded next to a river, although he only came to realize that he was a merman some time afterwards...