Christianity

Christianity, as portrayed in the 2003 Fullmetal Alchemist anime series is an ancient monotheistic religion. The followers of this ancient faith created the secret city that exists beneath Dante's lair and, as such, she and Hohenheim Elric may have been practitioners. However, all the adherents besides them had died out centuries ago, as had their system of time measurement based on the birth of their founder and icon, Jesus Christ. Although no one in the Fullmetal Alchemist series practices or even knows of Christianity, the town of Aquroya holds a church which seems to mimic some of the practices of the Christian church. The infamous thief Psiren spends a short time as a nun in this church.

In the manga, however, there's no mention of Christianity and, according to interviews gave by the author, Hiromu Arakawa, there's no christianity in FMA's world and, therefore, not christmas or any other religious holidays as well as no churches related to Jesus Christ. All religions mentioned in the manga were made up by Arakawa herself.