Puniru is a slime made by Kotaro Kawaii when he was a child and, for unknown reasons, came to life. It claims to be the cutest thing in the world.

Puniru's original form was a blue penguin with a hat, however, as the years passed and Kotaro began to pay less attention to Puniru, it decided to take the form of a cute girl in order to try to gain his attention again and make him call her cute. Her old penguin form is the shape of her side bag, where she keeps the ingredients to make more slime when she needs to transform. Despite her current form, Puniru has no gender.