Captain of the Special Search Unit of The Red Coats.

In a near-future Japan, Christmas has faded into myth, and the birth rate has dropped so dramatically that children are now the most precious commodity. Society has artificially extended adolescence to preserve their youth, and traditional holidays, like Christmas, are a mere legend of the past.
 
Volume 1 of SANDA introduces Sanda Kazushige, a middle-school student who unexpectedly becomes entangled in a strange and dangerous mystery. When his classmate, Fuyumura Shiori, accuses him of carrying a curse that could help find her missing friend, Ono Ichie, Sanda's life takes a dramatic turn. Together, they embark on an incredible adventure to unravel the truth behind Ichie's disappearance and uncover the hidden magic of Christmas itself.
 
As they delve deeper into the mystery, the duo faces external threats and internal challenges—questions about loyalty, courage, and the power of belief. Along the way, they confront the true meaning of friendship, trust, and the possibility of magic in a world that has all but forgotten it.
 
(Source: Titan Manga)

The story starts with Sanda, a second year middle school student, getting attacked with a kitchen knife by his classmate Fuyumura. While Sanda couldn't make sense of the situation at first, he gradually came to believe that Fuyumura's actions were just mean acts stemming off from the latter having a peculiar puberty phase.
 
But that is all a misunderstanding. Fuyumura actually suspects that Sanda is the descendant of a certain lineage...

Saburou Yagiuda