An Sakurai is notoriously known as the "Underground Doctor," operating predominantly in the dark underbelly of society as a surgeon for the criminal world. Her persona paints a terrifying picture: unhinged, sadistic, and psychotic. An's entire existence is fixated on a singular goal — discovering the key to immortality, and she will stop at nothing to unlock this coveted secret, displaying a level of ruthless determination and disregard for conventional ethics and morality in her pursuit.