Erica is a girl slightly older than Alita, who saved her from being shot by a Martian soldier and accompanied her partway across a minefield. She appears to be Alita's closest friend while they were both training as Künstlers, and was more confident and outgoing than Alita was. Erica Walt, is a surviving Künstler and member of the Einherjar, making her a necro soldier. She was Yoko's closest friend during the Terraforming Wars, during which both girls were orphaned and were subsequently taken into Grünthal. Erica surfaced during Operation Hagel as the mysterious Frau X, although her true identity was not confirmed until the events of Mars Chronicle.