Christmas

Christmas is an annual festival, primarily observed on December 25th. It is a Christian celebration, commemorating the birth of the Son of God, but the festival is also celebrated by many others across the world.

Santa Claus
Santa Claus is a figure commonly associated with the modern-day Christmas. He is said to be a jolly old man in a red suit who secretly delivers presents for good children while they are sleeping on Christmas Eve, riding through the skies on a sleigh drawn by reindeer. The character of Santa Claus is derived from several figures, including.

According to Leivinia Birdway, there is an organization known as the Nicholas Foundation (ニコラウス財団), presumably a secret Magic Side organization related to Santa Claus, which she briefly mentioned when she mistook the child Fremea Seivelun's comment that she knows Santa Claus exists as a deliberate reference to the organization. It is unknown whether the organization has an actual Santa Claus as Leivinia Birdway's reaction implies that the character Santa Claus exists. No other mention of the organization has been made since.

Homecoming Arc
Leivinia Birdway mentioned the Nicholas Foundation when she mistook Fremea Seivelun's comment that she knows Santa Claus exists as a deliberate reference to the organization.