Arc-En-Ciel

Arc-En-Ciel is a chimera creation of Promestein. She was specifically designed to defeat Granberia, easily overpowering the cursed swordswoman.

Trivia
Her name is French for rainbow, though how this relates to her character or design is yet to be seen.

Another possible explanation for the name is a degeneration of the word Archangel which is, when said, pronounced as Arc-En-Ciel. Also, given that an archangel as a "high-ranked" angel and should be the counterpart of Granberia, the strongest of the Four Heavenly Knights, it is likely that this monster is some sort of boss monster (not confirmed, so not categorized as one).