With all of the different jutsu shown in Naruto, one would imagine that weapons would really have no place among ninja. Yet it seems Sasuke is a fan, particularly of his sword, Kusanagi. Translating to "Grass-Mowing Sword," it went by the English name of Snake Sword and was used by Sasuke throughout Shippuden.
However, Sasuke's Kusanagi isn't the same one Orochimaru's seen using, but a replica. The Kusanagi Orochimaru uses is one from a real Japanese legend. It is one of the Three Sacred Treasures that make up the Imperial Regalia of Japan. The three treasures which, besides Kusanagi, include a mirror called Yata no Kagami (Eight Span Mirror) and a jewel called the Yasakani no Magatama (Eight Shaku Curved Jewel), represent three virtues: valor (the sword), wisdom (the mirror) and benevolence (the jewel). Each are presented to the ascending ruler during their coronation as Emperor.
The god Susanoo fought the eight-headed snake Yamata no Orochi, and the sword was found in one of the serpent's tails. Susanoo then presented the sword to the goddess Amaterasu as a gift to smooth things over after a past grievance between the two.
Orochimaru's Kusanagi was more powerful than Sasuke's and had many more natural abilities since it was the real Kusanagi from Japanese legend. He stored it in his mouth, where a snake would emerge and produce the sword. Orochimaru was then able to use the sword telekinetically and extend or shorten the blade at will. It could also cut through anything and transform into a small serpent. However, it could not damage Naruto's Four-Tailed form, which could be a callback to the original legend of Kusanagi, as the sword was found in the fourth tail of Yamata no Orochi. The fate of the sword is unknown, as it was sealed away with Orochimaru, but didn't reappear after he was brought back.
Given to him by Orochimaru, Sasuke's sword is a chokuto — a single-bladed straight sword — rather than a katana, as the original Kusanagi is. Sasuke's Kusanagi does not have any of the abilities that Orochimaru's does, like the ability to extend. It also doesn't have the ability to cut through any material, but Sasuke can channel his lightning chakra through the sword, increasing its strength and range. This also allows him to numb his opponent.
Itachi used the sword for a short while after his reincarnation during the Fourth Shinobi World War, using it in his and Sasuke's fight with Kabuto Yakushi. Madara later used it to mortally wound Sasuke by stabbing him through the heart. It was then discarded during their fight. Sasuke replaced the discarded sword with a new one sometime after the war's end, meaning that the one he uses now is not the original of the copy of Kusanagi. So, while Sasuke is shown with a sword in Boruto, it is not Kusanagi.
Much like Sasuke's training, the origin of Kusanagi surrounds Orochimaru, both in real life and the series. The sword was found in the tail of a giant snake, while a snake-person could produce the sword from his mouth in Naruto. Unlike its real-world counterpart, Kusanagi would be sealed away with Orochimaru, presumably to never be wielded again, even after his resurrection. Even the copy of it was lost in a pit of lava. It's probably for the best.
