|Anime Debut||Episode 23|
|Main Color||Black & White|
|Powers||Space Control (Gravity Control + Space Time Manipulation)|
|Burial Doll(s)||Misao Minakami|
English: Darker than the darkness emerging from the abyss...The shadow cast by the light of science...
Kurogane-Kai is made by Ania after Misao suggested combined the remains of Kurogane and Shirogane to create a new Asura Machina equal in power to Hagane. Kurogane Kai looks similar to Kurogane, but with parts of Shirogane on it. The first world's Ritsu comments that Kurogane-Kai's power output is even greater than Hagane's. Despite its power however, Kurogane-Kai was unable to close the gateway between the First and Second World until the First World's Misao sacrificed to power up Kurogane Kai. Kurogane Kai creates a condensed ball of gravity in its palm, then fires it through several spell rings which form a kind of barrel. Kurogane Kai showed a couple of new powers. These included being able to teleport itself, the Handler, and at least one other person a short distance away. Kurogane Kai can apparently also reach through space and time to retrieve a Burial Doll from inside its Asura Machina.
- Katana: Kurogane-Kai wields the same katana as Shirogane, it can manipulate space