Mai, a spirited student at the Santa Claus Academy, is assigned to rehabilitate Santa—a boy embittered by his Christmas-themed name and upbringing—by boosting his luck and outlook. Her magic specializes in conjuring items beginning with the Japanese syllable "san," though her spells frequently backfire, summoning unpredictable objects like samba dancers, salamanders, or sample dressing rooms, resulting in chaotic mishaps. While she initially presents as a cheerful junior high student, her form shifts to an adult version with heightened physicality and confidence, accompanied by a switch to the assertive masculine pronoun "ore," triggered by Santa’s growing belief in her mission.

Trained at the academy, Mai lags behind her accomplished rival Sharry, whose elite skills contrast with Mai’s erratic magic. When pressured to resume training in the second OVA, Sharry is dispatched to retrieve her, while Mai’s younger sister Maimai complicates matters by escaping the academy and unintentionally diverting retrieval efforts. Mai’s resolve to stay with Santa sparks clashes with Sharry and chaotic interruptions from Maimai, culminating in a farewell date frozen in time—a gesture rendered moot when the sisters’ mix-up nullifies the need for departure.

Mai’s bond with Santa shifts from relentless cheerleading to genuine affection, overcoming his initial resistance. She orchestrates a dual birthday-Christmas celebration, mediates his reconciliation with parents working abroad for orphaned children, and aids in delivering bespoke gifts globally, underscoring themes of generosity and Christmas’s spiritual roots.

Her Genki Girl exuberance drives slapstick antics and accidental fan service, including nudity during botched transformations. Her loyal reindeer Pedro amplifies both combat and comedy, wielding weapons like a three-section staff. Despite plot inconsistencies—such as ambiguities around her post-training gift-delivery capabilities—her story closes with her pledging to support Santa while maintaining her academy duties.