In near-future Japan with ultra-low birthrates, children are treasured but monitored. Santa is banned as dangerous. One snowy December 25th, middle-schooler Kazushige Sanda, descendant of Santa, is attacked by classmate Fuyumura who wants him to find her missing friend, Ono. "Santa, please find my friend." To protect children from adults, Sanda decides to become Santa and fight the adults.