Alter — Joan

A younger, comical "Santa" version exists, known as Santa Alter Lily.

Here is a helpful summary of her character and usage in FGO: Joan Alter

Based on the search results, "Joan Alter" (often referred to as or Jalter ) is a popular character from the Fate/Grand Order (FGO) mobile game and anime franchise. She is a distorted, "Altered" version of the historical Joan of Arc, appearing as an Avenger-class servant designed to be a vengeful figure. A younger, comical "Santa" version exists, known as