Misaki, a high school girl who loves tuna, is living with a mysterious girl named Maguro, who transformed from a yellowfin tuna into a human! Following the rules passed down in the tuna clan, Misaki tries to fend off Maguro's insistence to be eaten while searching for a way to revert her back to her original yellowfin tuna form. As their time together increases, the nature of their relationship gradually begins to change――