It turns out that Ernst is Geis' brother. At one time, he and Geis were members of the Clan of Darkness living in the Celcetan village of Danan, but he left with Gruda to the Romun Empire. Unlike Geis, who is trying to atone for the mistakes of his ancestors, he seeks to obtain the power of the Ark of Napishtim for himself.
Ys VI: The Ark of Napishtim
In the game proper, he sends out his three fairy homunculi, Jue, Sera and Xisa, in order to undo the seal on the ark and kidnaps Isha. Using the control key Almarion and Isha's power, he manages to gain control of the Ark, gaining jet black Eldeen wings in the process, but is ultimately defeated in a fierce duel by Adol, cracking Almarion's blade in the fight. After his defeat, Ernst tries to draw the full power of the Ark for himself, but the attempt overloads the already damaged Almarion. The control key shatters, causing the Ark of Napishtim to go berserk in the process. As he lays dying, he apologizes for his actions and asks Adol to stop the Ark, using the last of his stolen Eldeen powers to open the passage to the control room. He also bequeaths his three fairy homunculi to Geis.
- In Ys: Memories of Celceta, we find out that Ernst is originally from the village of Danan in Celceta. Also, Frieda, one of the party members in that game, was Ernst's former fiancée. He seems to have cared about her to a degree as he gave the homunculus Nina as a gift to her.
- Ernst appears to harbor many characteristics of the human antagonists that Adol faces throughout the series. He is a member of the Clan of Darkness (Gruda), hopes to awaken the sealed ancient artifact to obtain power (Dark Fact), and backstabs his superior to obtain said power (Chester Stoddart).
- Ys: The Ark of Napishtim Official Guide