Aki Kitsutaka

Touru's sister and former Burial Doll of Kurogane. She consumed all of her life force and vanished. Aki's death was the main reason why Tokiya and Touru wanted to destroy Second World to go to the Third World, a world where Aki exist. Kurogane Kai's two-sword skill reminded Tokiya of Aki and he muses that is Aki trying to stop him.

(First World)

A graduate of the Rakurowa high school who is a skilled swordsman. She saved Tomoharu and Kanade when stray Daughter attacked Kitsutaka residence. Aki later gives Tomoharu her necklace when Tomoharu decide to go back to the Second World.

-Wikipedia-