The circumstances of the knife's creation are unknown. It was given by the Fused Hnanan to Moash (later known as Vyre). Hnanan tells Moash that Odium has tasked him with killing a god; Moash then uses the knife to kill Jezrien. Moash removes the knife from Jezrien's body, but the subsequent fate of the knife is unknown. Moash notes that the Fused appear to be afraid of using the knife on Jezrien themselves.
The knife is a method to kill a Herald and trap their soul, preventing the Herald from returning to Braize as a "conventional" death would. Jezrien, while initially in a drunken stupor, quickly realizes that something about this death is different and claims to feel the knife drawing something from him into itself. Likewise Shalash instantly distinguishes it from previous deaths, as she could no longer sense Jezrien's soul. The knife "traps" the soul so it can't be reborn. This process operates under similar principles to the Scadrian manifestation of Investiture known as Hemalurgy, where practitioners are able to steal part of an individual's spiritweb using metal spikes. It would cause debate among cosmere philosophers whether the knife's magic properties are in fact Hemalurgy or rather a related, but distinct, phenomenon.
Following Jezrien's death, the sapphire set into the knife takes on a "subdued glow". The knife, when removed, trails dark smoke and leaves behind a blackened wound.
It has been theorized that the knife is made of Odium's god metal, citing its golden/yellowish-white color and the fact that Odium often manifests as a figure in gold and white and his power is often perceived as a golden light. The metal of the knife is described as unusually bright. Odium is active on Roshar when the knife first appears in the possession of one of his direct servants, and it is used for a task that Odium specifically requests.
The knife may share some characteristics with Shardblades, which cause a victim's eyes to turn black and burn out with dark smoke. Nightblood, an imitation of a Shardblade creating using Biochromatic Breath, leaks black smoke made of corrupted Investiture and can cause its wielder's body to turn black.
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--WeiryWriter (talk) 11:03, 11 March 2018 (MST)