"I'm cute no matter how I appear!" The protagonist and effectively the main character. First person: I (boku; cheerful, innocent). Seven years before the main story, a slime Kotaro made came to life, and they've been friends ever since. Originally, Puniru looked like a penguin, but since Kotaro (now a middle schooler) stopped calling Puniru "cute," Puniru took on the current form based on popular idols and other influences. However, Puniru seems unaware that this appearance causes the adolescent Kotaro a lot of trouble in various ways. Puniru can transform into any shape as long as there is laundry starch and borax water available.

The straight man of the series. A second-year student at Lime Private Middle School. According to him, he's just an "ordinary middle schooler," but... He was always with Puniru during elementary school, but now that he's in middle school, he often treats Puniru coldly. He seems bewildered by the lack of boundaries from Puniru, who follows him around in the form of a girl while maintaining the mentality of a toy. He has also publicly declared his unrequited love for Mami.

Kotaro's senior and a third-year student. A beautiful girl with long pink hair and a well-developed physique. Due to her height inherited from her mother, she secretly worries that few clothes fit her well. Because of her kindness to everyone and her saint-like personality, she is admired by all. However, her true nature is...

Kotaro's classmate. A boy with blonde hair in a ponytail. Kotaro doesn't think well of him, viewing him as a "flashy, annoying guy," and had heard rumors that he was quite the playboy. He has a frank personality, calling his senior Kira "Mami-chan" and suddenly calling Kotaro "Kotaro-chan," even though they weren't particularly close classmates. He actually seems to be on good terms with Kira, who calls him "Yusuke-chan." In truth, he loves the hobby anime "Monsura," which is popular among elementary schoolers. Since he has no friends in middle school who share his interests, he often plays with younger children. He turned out to be a "playboy" in the sense of being a hobby enthusiast (a CoroCoro kid).

The successor to the toy manufacturer "Cutieland." She has a strong obsession with "KAWAII" and engages in a fierce battle for the "Throne of Cuteness" with Puniru. She dotes on her favorite character, "Runrun," whom she designed herself. She feels envy and longing toward Puniru, a slime who possesses life and moves freely.

To fulfill Alice's wish, she builds "Runrun," a talking robot made from modified toys. To snap Alice out of her obsession, she challenges Kotaro and Nanba to an "Art Battle."

Identity: Originally a mascot character (mass-produced AI toy) created by Lady Alice Magane. Origin: In response to Alice's wish to talk and play like Puniru, Runru gained a unique personality and form by absorbing the power of the maid Houda and Puniru's slime cells. Role: Alice's exclusive attendant robot and support. Runru possesses strong loyalty to Alice and great courage. Recently granted emotions by Puniru.

Appearance/Position: A middle-aged man who looks like a scientist, with white hair, stubble, and a lab coat. He is a teacher at Lime Middle School. Goal: Originally a scholar researching autonomous slimes, he was expelled from his academic society for unpaid membership fees. Therefore, he plots to capture and study Puniru, the one-of-a-kind slime lifeform, to return to the academic world. Mad Scientist Side: He views Puniru not as a "cute girl" but purely as a "slime (research subject)." Because his intellectual curiosity is too strong, he has shown extreme behavior, such as trying to cut Puniru into small pieces or attempting to drop Puniru from the school roof for a durability experiment. Private Life: While he is one of the most eccentric people in the story, he is actually a married man and a devoted husband. He has a family consisting of his wife, Romi, and his son, Shuto.