The real name of the killer is the mysterious Heroine X, also known as Heroine X and only X, an unknown heroine who was tasked with eliminating the Saber-class heroines during Back Alley Satsuki - Chapter Heroine Sanctuary. With the codename "AX", X was a stranger who hailed from the "mysterious dimension" called the Servant Universe. Seeking to fulfill her "true and dearest wish" to "defeat all the Sabers", she brandished Secret-Calibur and left her hometown, leaving behind a "expression full of bitterness"
Even before reaching Chaldea, he managed to save an ancient royal dynasty from a crisis, resolve the internal struggle of the "Union of Integration of Humanity" and defeat invaders from another universe, but such actions were trivial enough to that she doesn't even remember having achieved. they. She will continue to swing her sword until her objective is completed, and she can still be seen "crossing the sea of stars" even today. Whatever happens, she also plans to take down the "Great Golden Emperor Cosmo Gilgamesh