GhostDevil

The Ghost Devil is Himeno's contract. She paid for it with her right eye, and she keeps it wrapped around her right arm like a sleeve of black smoke. When activated it extends into a massive phantom arm that can crush, grab, or strangle anything she points at. In its full form, which requires her entire body as payment, it becomes a column of smoke the size of a building. She uses that form once, in episode 8, to protect Aki from Katana Man. It is also how she dies.

The devil itself outlives her by four episodes. Akane Sawatari ends up holding the leash during the final raid and sends it to kill Aki. Instead the Ghost Devil pauses in the middle of the fight, lights a cigarette, hands it to Aki, and lets Himeno say goodbye through its smoke. Aki kills it the second she is done talking.