Keito

- Will/Gem:
"The Despised Mirror" Eyes Meteorite.
"Six-way Flawless Flames of Calamity" Perfect Star Sapphire.
"A Glittering Disaster Against the Covetous, Brilliant Extant Hometown of Nothingness - Rubra Melia Serpentes" Dead Serpent End Brilliant Wonder World.

She was the Queen Euryale, who got turned into an ugly sapphire serpent by the ugly Empress Palace.
After death, her Dying Will was left behind in the veins of land throughout Phrygia. After a vein of land parts were brought up to the surface, Euryale appeared before Arianna and others, seemingly given an order to "put an end to the war."
However, it is later known that Keito has materialized in every turning point in history, being the background causes of conflicts. She also caused the Seven Years War by killing Elisha, a sub-leader who founded Medusa organization.
She tried to end wars by doing the reverse, which is causing conflicts between species to decrease population. Once every lifeform would be exterminated, she would be able to build a world of only herself.