In a future where children are few and regarded as Japan's most valuable assets, Christmas has become a mere legend of the past. For the students of Daikoku Welfare Academy—a boarding school where they are educated, protected, and monitored—the mythical Santa Claus is a forgotten character of fiction. For the adults, Santa Claus is a very real menace that needs to be neutralized by the Saint Nick Pursuit Unit in case he makes an appearance.

Shiori Fuyumura, a student of Daikoku Welfare Academy, is determined to find her best friend, Ichie Ono, who has been declared dead after being missing for six months. One morning, Fuyumura summons her fellow class representative, Kazushige Sanda, only to attack the unknowing boy. She is convinced that Sanda is the descendant of the infamous Santa Claus—the only person who can make her wish of finding Ono come true—and is determined to force out his dormant true self by any means necessary.