The Nobitsure Kage is an ancient sword capable of killing the Ancients, immortal demon rulers of Shadow Realm. The Ancients cannot touch the Nobitsura Kage as just touching the weapon can kill them. The sword has incredible power, as just slashing with it unleashes a wave of energy capable of instant killing any lesser demon. For safety reasons, Nobitsura Kage was divided into three separate swords and hid all over the mortal world.
Thousands years ago Hoji using Itsuse no Mikoto's body forged the blade so the Ancients could seal the gates with soul of their own and this way seal the Outer Gates, so their enemies couldn't reach Shadow Realm. After the ritual was done, Ituse no Mikoto kept the sword in case Ancients broke the promise to never attack mortal world. He then split it into three parts, gave the parts to three horsemen and ordered them to hide them so no one could ever find them.
Before Shadow Warrior
After Ameonna is poisoned, Enra sees, that only the sacrifice of an Ancient could revive Ameonna and save the Shadow Realm, and thus searches for the Nobitsura Kage, the only thing in existence which can kill an Ancient. Enra brokers a deal with the mortal Zilla to find and assemble the sword, promising a cure for his paraplegia and the assistance of demons to conquer the Earth.
Shadow Warrior (2013)
Over the course of the game, Lo Wang manages to reassemble the Nobitsure Kage and storms the Shadow Realm with the intent to kill Enra. Lo Wang corners Enra after a tense battle with Xing's headless body, Enra allows Lo Wang to slay him, since he is the only sacrificial candidate left. The sword is last seen laying near Lo Wang.
Shadow Warrior 2
After Wang used the Nobitsura Kage to kill Enra, the sword started to shrink in size and lose it's former power. When Master Smith finds out about this, he offers his help to fix the sword to it's former state. To do this, Smith asks Lo Wang to retrieve scrolls containing the information how to reforge the sword. Lo Wang agrees and goes to Smith's grandfather's house for ancient smithing scrolls. When Lo Wang gets there, the scrolls are missing, stolen earlier by looters.
Smith then sends one of it's pupils to dig for the information of the scroll location. When the pupil goes missing, Smith sends Lo Wang to find him. Wang finds him and finds out from Hideo that the scrolls were sold to four different vendors in town. Wang then sets off to get them back. He reaches a vendor named Saito who tells him that he already sold the scrolls and reveals the location of the buyer. He reaches the antique dealer and retrieves the smithing scrolls. Smith can't reforge the Nobitsura Kage and instead turns it into a medallion, which can be used on another sword.
- The rough translation of Nobitsure Kage from Japanese would mean "Shadows Even Burn", Kage=shade, sura=even, Nobi=burning off the fields. This refers to the blades ability to burn shadow beings.