Outer Path

King of Hell, a technique, used by the Naraka path, that summons a giant demonic figure for the apparent use of interrogation. It is capable of discerning whether an individual is lying or not. When implemented on a target, a serpent-like apparition of their life force energy emerges from their mouth and presented to the figure. The King of Hell then proceeds to pass its judgment on the victim. If they are lying (or refuse to answer the question), their life force energy is consumed and they die. If the target is telling the truth, they don't die, though they're left extremely exhausted. When the Naraka path uses this technique, the figure possesses the Rinnegan eyes similar to how the Animal path's summons all possess the Rinnegan. The King of Hell can only be seen by the ones it's being used upon.

As a secondary ability, the King of Hell can re-infuse new life force energy to the dead body it eats. When it consumed the remains of the Asura path, the Path emerged from the figure fully restored and is even wearing new Akatsuki robe (the body had discarded its previous robe). Once Naraka path uses this technique, he needs time to recharge and possibly cannot use King of Hell at all. While the King of Hell is being used for revival purposes, it seems that others are able to see it, unlike when it is being used for interrogation purpose. However, it was Naruto in Sage Mode that was able to see it, so it is possible that normal people cannot, even for revival.

The King of Hell can be summoned when the Outer Path: Samsara of Heavenly Life Technique is used, where Nagato can release life force energy to people who were recently killed, allowing their souls to return to their rejuvenated bodies.

Trivia

 * The King of Hell, Yama, is the judge of the dead in the Buddhist religion. He decided if someone stayed dead or returned to the world of the living, and would choose how they would be reincarnated. It's believed that if you lie to him, he will rip out your tongue.
 * The black flames that surround the base of the King of Hell is identical in appearance to those of Amaterasu and of the Blaze Release.