In a future where children are rare and considered Japan's most precious assets, Christmas has faded into a 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 figure of fiction. To adults, however, Santa Claus is a genuine threat that must be neutralized by the Saint Nick Pursuit Unit should he appear. Shiori Fuyumura, a student at Daikoku Welfare Academy, is resolved to locate her best friend, Ichie Ono, who was declared dead after disappearing for six months. One morning, Fuyumura summons her fellow class representative, Kazushige Sanda, only to attack the unsuspecting boy. She is convinced that Sanda is the descendant of the notorious Santa Claus—the only person capable of fulfilling her wish to find Ono—and is determined to force his dormant true self to emerge by any means necessary.