In the anime adaptation, Eibon allies with Arachne 800 years in the past to cure his lover from a fatal illness and, after failing, transforms himself into a demon tool used to unlock Brew as penance.
Eibon allies with Arachne 800 years in the past to cure his lover from a fatal illness and, transforms himself into a demon tool. This is after failing. This is in the anime adaptation. This demon tool is used to unlock Brew as penance.