"Itsudatte My Santa!" is a short anime series that blends elements of romance, comedy, and fantasy. The story centers around Santa May, a young girl who claims to be a Santa Claus apprentice. She appears in the life of a high school student named Minoru Uesugi, who has lost his Christmas spirit due to a tragic childhood incident involving his parents. May is determined to restore Minoru's belief in Christmas and fulfill her mission of spreading joy.

Minoru is initially skeptical of May's claims, dismissing her as delusional. However, as May persistently tries to bring happiness to those around her, including Minoru's childhood friend Mai, her sincerity begins to break through his cynicism. The narrative explores themes of healing, forgiveness, and the importance of cherishing meaningful relationships. May's efforts to help Minoru confront his past and rediscover the joy of Christmas form the emotional core of the story.

The series also introduces other characters, such as Mai, who harbors feelings for Minoru but struggles to express them, and May's rival, Santa Gora, who challenges May's methods and beliefs. The interactions between these characters add depth to the narrative, creating moments of humor, tension, and heartfelt emotion. The story unfolds over a concise runtime, balancing lighthearted moments with more poignant reflections on the significance of Christmas and human connection.