Potemayo's story revolves around Sunao Moriyama, the male protagonist, who is a junior high school student. One day, while eating breakfast, Sunao hears a noise coming from his refrigerator, and opens the door to find a small, cute creature inside which has trouble talking. While deciding what to name it, Sunao looked down at one of the foods he was eating, which contained potatoes and mayonnaise, and decided to name her Potemayo. Sunao decides to take Potemayo with him to school that day, and discovers that Potemayo is an instant hit on the members of his class, especially the girls. While Sunao is at school, another similar creature comes out of Sunao's refrigerator, and ends up making its way to school. One of Sunao's classmates, Ky? Takamimori, finds the creature and names her Guchuko. Unlike Potemayo, Guchuko is much more violent and will often shoot beams of intense energy out of two horns on either side of her head.