First the opponent must be trapped in the torso of Kuroari. After this is accomplished, Karasu separates into eight components. The torso is left behind while the arms, legs, and head are positioned around Kuroari, each with a sharp blade. Kankurō guides the separate pieces into slits in Kuroari's torso, impaling the victim inside.
The name of this secret technique is a play on a popular Japanese toy "Kurohige Kiki Ippatsu", in which the goal of the toy is to stick little plastic swords into a barrel to make the pirate in the centre jump out.
This technique follows a couple of Magiciansstage tricks, called; "Devil's Torture Chamber", and "Impalement" and other Penetration techniques: except in the case of the Black Secret Technique: Machine One Shot, it doesn't create the illusion of being stabbed or impaled, the unfortunate victim actually does get impaled.
The English name of this technique is a reference to the iron maiden, a coffin-like torture device with sharp spikes lining the inside. A victim is forced to stand straight up inside until they can no longer support themselves, at which point they are forced to lean forward or backward onto the spines, resulting in a slow and painful death.