User blog comment:Brobuscus101/Top 32 Season 2 Death Battle Episodes/@comment-25430354-20160215194837

"Inferno is a demon made of fire, how do you cut through that?" It is in canon that Inferno has been cut through, and not just by Soul Calibur. Siegfried defeated Inferno in the original Soul Edge with his giant sword. Guts has better stats and feats than Nightmare all around, the Astral Plane explanation just made it sure that Guts would successfully kill Nightmare, similar to how some stuff is like "only the Master Sword can kill Ganon."