Naraku is regarded as one of the most legendary swords in all the world. It is one of the twelve Saijo O Wazamono, existing as both a "Black Sword" (黒刀, Kokutō) and a "Cursed Sword" (妖刀, Yōtō). This blade is currently owned by Altanae Stark.
The black sword "Naraku" has a rather modest design to it, unlike many others of the Saijo O Wazamono collection which are generally ornately decorated, appearing to have the classic appearance of a nodachi. It has a firm handle that is comfortable to wield, a black crossguard in the shape of a manji which accents the pitch-black blade that carries with it an extraordinary strong sheen. It is said that both Naraku and Yoru were forged at around the same time by the same swordsmith, making them brothers, and that they have clashed together countless times.
Naraku, much like every sword among the Saijo O Wazamono, is a unique sword in that it was forged in the presence of an intense Haki which stained the blade black. As such, the sword itself carries an intimidating presence, similar to that of Yoru, which requires a tremendous degree of willpower and fighting spirit to successfully wield. Naraku almost seems to have a will of its own, as Altanae stated the blade will refuse to be wielded by anybody it deems unworthy and that its holder must possess, not only an incredible willpower that offsets the blade's own will, but a heart that seeks the ultimate form of freedom.
According to Altanae, the Naraku was wielded at one time by the legendary pirate, Shanks, and was used to duel against Dracule Mihawk who had wielded the Yoru. After Shanks had lost one of his arms and a considerable degree of his fighting spirit, Naraku refused to be wielded by him and could also explain why Mihawk had lost interest in settling the score with his former rival. It would eventually find its way handled by many swordsman who knew of its legend but believed themselves worthy, only to fail and lose their hearts to the blade's overwhelming presence. Among them, the one who would eventually manage to subdue the blade's will into submission was none other than Altanae himself.