Esta es la historia de Puniru, una slime, y Kotaro, un chico de instituto que es su mejor amigo. Tras siete años siendo mejores amigos, un día, Puniru se convierte en chica y prova que la relación entre los dos cambie. ¿Cómo se tomará Kotaro la nueva forma de la que era una slime?

Kirara, la chica más guapa de la escuela, es la persona más buena de todos quienes pisan ese edificio. Para llamar su atención Kotaro pide a Puniro que se transforme, pero su cambio físico provoca reacciones en el resto de estudiantes e incluso de algunos profesores.

Kotaro acude a una cafetería en la que hay una colaboración con su personaje favorito. Se supone que va a pasar un rato divertido y entretenido, pero Puniru no duda en acompañarlo.

Alice, granddaughter to the president of the toy company that made Kyuthi-chan, challenges Puniru to see whether she or a character Alice created is more adorable—and you could say the competition gets blown into gigantic proportions!

In an attempt to please Alice, Hodai dons a Runrune costume. Meanwhile, Nanpa, Puniru, and Hone-chan fight over Robo Runrune. Then, to put some pep back in the exhausted Kirara-senpai’s step, Puniru and Runrune become cheerleaders.

Puniru gets moldy and down in the dumps when Runrune starts ignoring her. Later, she’s determined to get Runrune and Alice to be friends again. Next, AI Runrune hits the scene, and Alice and Puniru face off to see which Runrune is better.

Kotaro and the boys go to the beach for a day of fun while Puniru and Kirara-senpai are at the school pool. Later, Kotaro asks Puniru to help him cool off with a special transformation, the gang hits a café, and then it’s time to tackle summer homework.

It’s time for the school festival, but Puniru and Alice get into a fight over Kotaro. Alice tries to win him over with an incredible offer, and Puniru tries to throw the match so he can pursue his dreams.

Kotaro wants to be cool and decides to try his luck with dragons and a rock band. Puniru then lets the cat out of the bag about Kotaro’s feelings for Kirara, which forces him to make a move. Can he get Puniru to help him out?

Ever since being teased as kid for liking cute things, Kotaro has never enjoyed Christmas. This year his parents are going on a trip for the holiday, so in order to avoid being stuck home alone with Puniru, he tries to throw a Christmas party.

Puniru says she’ll spend the holiday with whoever brings her the cutest Christmas cake, but the offerings she gets are... interesting. When a certain someone loses their patience, she may yet get a Christmas to remember.

Out of the blue, Kotaro wins tickets to a ski resort—specifically the Runrune Resort run by Alice. When they get there, Puniru is determined to make an impression, and her desire to be cuter than ever may just spur even greater adventure.