In the year 2080, the world is like it is now, yet different. Government-arranged marriages, elaborate plastic surgery, and medical science are at the forefront of Japanese society.

Sanda Kazushige is a middle-school student who hasn't quite matured, despite being in the thralls of puberty. Put into a life-threatening situation by his classmate Fuyumura, Sanda discovers his uncanny ability to turn into a burly (and more grown) Santa Claus, and is thrown into a world of chaos to save his fellow students in only ways Santa Claus can do, while trying to solve the mysteries of the school he attends and the truth to where his supposedly-dead classmate Ono went.