Peterhausen, Ichiban Ushiro no Daimaou Wiki

Peterhausen first appeared in the series on episode 5 trying to kill Etou. Later in the episode, Sai defeated Peterhausen while saving Etou making Sai Peterhausen's master. Peterhausen is a dragon formed by the first demon king. He died in a war with his master. the current demon king in the series, Akuto Sai. Before Peterhausen died, he bit off his tooth as a remembrance gift.

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Peterhausen, Ichiban Ushiro no Daimaou Wiki

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Catching up with the Demon Lord Ambivalence , or is it ambiguity?

Fujiko Etou from Demon King Daimao