Eiha
エィハ
She is known as a Bounded One, which makes her bound to a monster or demon named Val. Eiha is Ibuki’s guardian but wants to be his sword.
Ibuki says Eiha is the most precious person to him when he used her as a offering to the Red Dragon in episode 12. In the end it is shown that her and Val’s life were fused into one life.