Sigrune

Svahhildes elder sister who turned into a Black Valkyrie after her Valhalla was destroyed. Sigrune was a promising valkyrie who was ready to achieve the rank of Hilder. However she turned into a Black Valkyrie before that could happen her Valhalla destroyed and her hero lost forever. Shrugging off lesser Valkyrie with ease she was finally ejected out of the heavens by Grimhilde and her hero Slayburg. She was not killed however so she would eventually become a demon lord. Source: The Fifth Heaven of Hlodj