Nikko

One of the only two swords in Rance world that can harm demons and demon king. She is one of the legendary five that challenged demon king Gele 1500 year ago. She was a samurai before turning into sword form.

Nikko can take human form as seen in Kichikuou Rance. This lead to the theory that Chaos can also turn back to human form at will but maybe he have some reason not to do so.