Welvath was a female demon with long blonde hair, sharp teeth and a tentacle replacing her right eye. Her arms split down the middle on each side with a mean set of jaws inset on each, and her breasts formed into disfigured faces with long forked tongues.
Welvath could presumably attack with her clawed arms, and bite with her not so beautiful breasts.
After Akira Fudo and Ryo Asuka attempt to summon demons to a Black Sabbath in order for them to merge with a demon themselves, the guests angrily turn on the two and start to beat them after Ryo had attacked them.
However said guests then start to merge with demons, starting with a woman merging into Welvath in a prolonged, grotesque sequence of transformation. Around her, others begins changing and its not long till Akira transforms into Devilman by fusing with the devil hero Amon. Welvath see's this and lunges at him but her head is grabbed by Akira, who twists it till it bursts from her neck before crushing it.