Lord El-Melloi II Case Files character. A Servant summoned by Dr. Heartless. She is considered to be Iskandar's Shadow, and is actually Hephaestion's younger twin sister who worked as Iskandar's body double. Due to her lack of a proper name and identity, she is not seen as part of Ionioi Hetairoi.
She was released in Fate/Grand Order as a Pretender-class Servant, going by the name Hephaestion.