Igzasion

Igzasion is an ultimate sword and supposedly the only weapon capable of slaying the Demon Lord. It was Elulu's fate to sacrifice her life to become the sword, which can only be forged from the blood of a dragonkin girl with human appearance. However, Seiya and the gang think sacrificing a young girl's life is too insane a price to pay. Seiya instead saves Elulu from Queen Leviae.

Seiya then creates a platinum sword from the pit Leviae dies in as well as swiping a drop of blood from Elulu. Seiya tricks the dragon kingdom into thinking it is the real Igzasion to put their minds at ease, saying that Leviae would have wanted to sacrifice herself to save Gaebrande anyways.

Seiya ultimately finds another way to defeat the Demon Lord, by casting Valhalla's Gate twice.