Nico's sword is a three-foot-long black sword forged from Stygian iron that has the power to suck away its victim's essence. Nico di Angelo acquired it sometime between The Titan's Curse and The Battle of the Labyrinth. The origin of the sword is currently unknown, but there is a possibility that Nico forged it himself in The Battle of the Labyrinth when he is seen in a camp ground near the River Styx.
Hazel Levesque, Nico's sister, mentions that she at first didn't think much of it, though that was before she'd seen it in action. Nico is seen wearing the sword while meeting Percy in Camp Jupiter, and he leaves it outside of New Rome with Tiberinus while participating as a senator. He later take it with him when he embark upon a journey to locate the Doors of Death from inside the Underworld, and manages to take it with him while falling into Tartarus.
Hazel uses her sense of Underworld metals to try and track down her brother, who has been captured by the giants. Unfortunately, Gaea separated Nico and his sword to lead his friends Frank Zhang, Hazel Levesque, and Leo Valdez, who were attempting to rescue him, into a trap.
Percy Jackson describes it as being, "black as a nightmare and truly frightening." It is noted to glow with a faintly sinister purple light.
- Nico uses it to summon as well as banish the dead by stabbing it into the ground.
- The sword sucks the essence of the killed monster into the sword, so the monster stays in Tartarus longer or prevents them from reforming.
- The sword strikes fear into its owner's enemies.
- The sword seems to "make shadows even gloomier, as if the infernal metal was soaking the light and heat out of the air", according to Jason Grace.
- It is unknown whether the sword itself has necromancy, or Nico simply uses it as a means of channeling his power.