Mami Kirara is a third-year student at Lime Private Junior High School and later advances to high school, making her the senior of protagonist Kotaro Kawaii, who harbors a long-standing crush on her. She is widely regarded by her peers as a saintly figure due to her consistently gentle and caring nature, and she is admired by everyone in the school. However, her public persona of calm kindness contrasts sharply with her private self, where she reveals an energetic and sometimes untamed personality. She has a deep love for sweets, powerful motherly instincts, and a tendency to act on impulse, often throwing herself into helping others even at the cost of her own well-being, as seen when she overworks herself to prepare for school events. Her speech is marked by a relaxed, drawn-out tone, often ending phrases with sounds like dawa~ and noyo~, which suits her outwardly placid demeanor.

Mami has long pink hair, usually styled with braids on the sides, and wears a red and yellow headband. She maintains a relaxed, often cheerful expression. Her motivations are rooted in a genuine desire to support those around her; she acts as a nurturing presence and takes on motherly roles within her social circle. In the story, she serves as the romantic interest for Kotaro and a foil to Puniru, the shapeshifting slime girl. Puniru perceives Mami as a rival for Kotaro’s attention, though Mami herself treats Puniru with kindness and finds her various forms charming. She lacks any supernatural abilities, being an ordinary human who brings a grounded, everyday perspective to the series’ comedic and fantastical events. Her relationships are defined by her saint-like reputation: she is beloved by classmates, respected by teachers, and viewed with affectionate awe by Kotaro. Over the course of the series, she remains a consistently supportive and stabilizing figure, with her hidden wild side occasionally surfacing to add unpredictability to her interactions. Her development is subtle, mainly seen in her deepening bond with Kotaro and her growing familiarity with Puniru’s unusual nature.