Joan Alter -

As an Avenger, she is a high-damage dealer, often noted for having some of the highest Attack (ATK) values in the game. Key Skills (Leveling Priority):

Born from a wish upon the Holy Grail by Gilles de Rais, she represents a twisted version of Jeanne d'Arc seeking revenge. Over time, she develops into her own person rather than just an imitation of her saintly self. 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. As an Avenger, she is a high-damage dealer,

A younger, comical "Santa" version exists, known as Santa Alter Lily. Based on the search results, "Joan Alter" (often

She is a heavily featured character in fan art, merchandise, and cosplays.

Boosts critical damage (+50%) and star gathering rate for 3 turns (ideal to level first).

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