Born on December 24, the character’s name directly references his birthdate, chosen by parents who prioritized their wedding anniversary over his birthday, leaving him isolated each holiday season. Perceived neglect and societal mockery over his name fueled a bitter resentment toward Christmas. His childhood lacked traditional festivities, marked only by a recurring gift: a photo of his parents surrounded by unfamiliar children, deepening his abandonment.

The manga attributes his parents’ annual absence to anniversary vacations, framing his anger as a response to their indifference. The anime OVA reimagines their absence as humanitarian efforts abroad, aiding impoverished children. During a workplace visit, he confronts their altruistic motives, complicating his resentment with reluctant understanding.

Mai, a trainee Santa Claus, enters his life determined to revive his belief in Christmas through magic tied to "san"-prefix words, though her early spells humorously summon only fish. Her unwavering empathy gradually challenges his cynicism. A turning point arrives as he witnesses his parents’ sacrifices, thawing his hostility.

A second OVA leaps forward in time, exploring summer months where Mai’s potential departure forces unresolved tensions about their bond. Amid comedic mishaps, he tentatively embraces vulnerability. By the story’s close, he reconciles with his parents’ choices and accepts Mai’s role in his life, symbolizing his shift from isolation to connection.

While the manga focuses on parental neglect’s psychological toll, the anime expands his growth through external influences, illustrating a nuanced arc from bitterness to cautious emotional openness across differing narrative scopes.