This is the story of Puni the slime and Kotaro the middle school student, until they are no longer friends... Kotaro Kawaii is a boy in his second year of middle school. When he was in elementary school, the slime he made came to life, and for the seven years since then, he and the slime, who he named Puni, have been spending their time together as "friends". However, Kotaro has one problem... As they have both grown up over the seven years, Puni has transformed into an incredibly beautiful girl! In addition to her beautiful appearance, Puni transforms into all sorts of cute forms as a slime, and her carefree behavior makes Kotaro's heart pound and he is at the mercy of her every time. Will Puni and Kotaro be able to spend their days together as "friends" forever?