Sasuke Uchiha is one of Naruto's finest fighters and among the most important characters in the story. Being an Uchiha, Sasuke was destined for greatness from the beginning, and the fact that he was a main character only made him that much more relevant. Kishimoto, Naruto's author, often describes Sasuke as the Yin to Naruto's Yang, meaning their importance to the story was almost equal and when one got stronger so did the other.
Sasuke's growth as a shinobi was particularly boosted when he left Konohagakure to seek power from Orochimaru. During those two and half years, Sasuke grew dramatically in strength and acquired skills that far surpassed that of Naruto Uzumaki. At the same time, something interesting that he also acquired during this time was the Sword of Kusanagi – a sword that would go on to become his trademark weapon for the rest of the series.
The Power Of The Kusanagi Sword
Sasuke Uchiha got access to the Kusanagi sword at some point during the time skip. The first time fans got to see the sword was when Team 7 finally met with Sasuke after tracking down Orochimaru's hideout. What followed was the very first meeting of Naruto and Sasuke after the time skip and, along with it, a true demonstration of how strong Sasuke had become.
Sasuke didn't hold back using the Kusanagi sword during this confrontation and showed fans exactly what he was capable of. By channeling Chidori through it, he claimed that his sword was simply unblockable. When tested against Yamato, the sword was powerful enough to break a kunai in half and even pierce through the powerful Wood Release Kekkei Genkai.
Interestingly, Sasuke's sword shares its name with Orochimaru's trusted blade, also known as the Kusanagi Sword. By the looks of it, the two swords differ quite a lot in both looks and their powers. Orochimaru's sword looks far less like a chokuto and also possesses special properties. In particular, his Kusanagi sword is known to have a reputation of being able to cut through almost anything with ease. At the same time, it could also extend and retract in size on Orochimaru's command, as seen during his fight against Naruto Uzumaki. Furthermore, Orochimaru could also control his Kusanagi sword telekinetically, which is nothing short of incredible.
Sasuke's Kusanagi sword, on the other hand, didn't have any of these powers. The sword was, more or less, a regular sword, however, its only known power was that it is considered to be unblockable, initially, at the very least. As the series went on, Sasuke's unblockable sword became blockable and the many fights that he fought are proof enough of that. Despite that, the blade was much stronger than the average sword, especially when Sasuke ran Chidori through it.
In fact, with Chidori running through the sword, Sasuke could even cut through the Kubikiribocho, which is one of the seven greatest swords of Kirigakure, wielded by the infamous Seven Swordsmen of the Mist. At the same time, Sasuke could even paralyze those who were struck by this blade, making it even more useful.
What Happened To The Kusanagi Sword?
Sasuke's used the Kusanagi sword extensively after the time skip in the story right to the end of the Fourth Great Ninja War. After Madara Uchiha stabbed him in the chest with his own sword, Sasuke passed out and had to be rescued by Kabuto Yakushi. Shortly afterward, he met Hagoromo Otsutsuki and received half of his powers and this strengthened him tremendously. Strangely enough, Sasuke stopped using his sword shortly after that. Perhaps this was because he didn't need the sword, or maybe the urgency of the situation required Sasuke to tackle the threat of Madara Uchiha anyhow.
Either way, Sasuke stopped using his Kusanagi sword after stabbing Madara Uchiha with it once. In the fight against Kaguya Otsutsuki, the scabbard of the sword was lost as well, which meant Sasuke had now lost the sword completely. Interestingly, Sasuke didn't look any weaker in the fights that he fought without the sword. Against Kaguya Otsutsuki, he was fairly impressive and managed to hold his own and against Naruto Uzumaki, Sasuke did just as well as his opponent. While having a sword certainly would've offered him some advantages, Sasuke's versatility as a fighter was on full display as he was just as great without it.
After the Fourth Great Ninja War, Sasuke ended up replacing his blade with a sword identical to the Kusanagi as was shown to fans in The Last: Naruto the Movie. While there is a chance that this sword was the very same that he carried in the Fourth Great Ninja War, the fact that the scabbard was destroyed seems to imply that this sword was completely new, yet identical.
Sasuke's Sword In Boruto
In Boruto, Sasuke has a completely new sword and according to the eighth supplementary guidebook/databook of Naruto, called Zai no Sho, this sword is also called the Kusanagi sword. Whether this sword is just as powerful as his old sword remains to be seen, however, he did use it against the likes of the Otsutsuki and fared amazingly, which implies that it is stronger, if anything. With it, Sasuke managed to cut Kinshiki's horn with ease, and even match Isshiki's rods. It is no surprise that Sasuke excels at the usage of his sword and fans will, undoubtedly, see more of him with his trusted blade in Boruto.