The Shadow Sword (降魔の剣, Kōma no Ken, literally translated as Sword of Demonic Invocation, VIZ translation, Conjuring Blade) is one of the three Artifacts of Darkness. The sword is crafted from a toxic stone, and a single scratch from this weapon transforms the victim into an E class demon; most likely a cultivated human. Only a special antidote, found in the sword's hilt, can reverse the demonification process. The blade's transformation power has no effect on other demons, as evidenced when Kurama was stabbed by it, and he did not turn.
Hiei was the one to steal this from the Spirit World vault, but was later returned when he lost to Yusuke. However, as the blade was coated in Kurama's blood, King Enma learned that the artifacts were stolen and spanked his son for it.
- The Shadow Sword is based on the Kusanagi (草薙の剣, Kusanagi-no-Tsurugi, literally translated as Grass Cutting Sword), one of the three sacred treasures of Japan. Coincidentally, Hiei mistakenly stabs Kurama, who would later be revealed as a plant manipulator, with the sword.
- The blade does not affect demons (as they are already demonic), but also doesn't seem to affect humans with souls of demons (i.e. Kurama).
- In the official Funimation website, a picture of Hiei with his normal sword is mistakenly labeled as the Shadow Sword.