The Sandai Kitetsu is one of the Grade swords. Like all of its predecessor Kitetsu swords, this one is said to be a "Cursed Sword/Blade" (妖刀, Yōtō?).
1 Cursed: Shodai Kitetsu
The first forged Kitetsu blade, known as the Shodai Kitetsu is the strongest out of all three of them. This sword is one of the Saijo o Wazamono grade swords, making it one of the 12 strongest blades in the entire One Piece series.
Kokuto Yoru (aka Black Blade Yoru) is currently the strongest sword in One Piece. It is befittingly in the hands of the greatest swordsman in the world, Dracule Mihawk. Yoru is graded as one of the 12 Supreme Grade swords, the highest quality swords ever created in the One Piece universe.
The highest grade swords are called Saijō Ō Wazamono. The swords belonging to this category are the rarest. It is followed by Ō Wazamono, Ryō Wazamono, and Wazamono.
Sandai Kitetsu
This sword is considered to be cursed (as recognized by Zoro) and is said to bring tremendous misery to its owner. Zoro tested his luck against this cursed sword, though, by throwing it up in the air and holding his arm out. He wanted to see if the sword could cut off his arm.
Along with Wado Ichimonji and Sandai Kitetsu, Shusui once again completes Zoro's three swords. However, it's traded for Zoro's next sword.
In the anime, Luffy managed to use it to cleanly cut through multiple swords with great ease despite his lack of skills. Like all of the swords crafted by members of the Kitetsu school, this one is said to be cursed and will bring a horrible death to all of its owners.
Zoro liked the concept and decided to test his luck against the curse. He threw it into the air and held out his arm, willing to let it cut his arm off. Zoro's luck won and the blade circled neatly around his arm. The shop owner gave Zoro both Sandai Kitetsu and Yubashiri for his skill and luck.
As one of the 50 Skillful Grade Swords, Yubashiri was a rare and reliable weapon that served Zoro's unique fighting style well. It was destroyed during Zoro's fight with Shu on Enies Lobby, and was later left alongside the Rumbar Pirates' gravesite on Thriller Bark.
The Wado Ichimonji is a sword of great personal importance to Roronoa Zoro. It was forged by Shimotsuki Kozaburo and was once a prized heirloom of his family. It is also one of the 21 Great Grade swords. After the death of its previous owner, Kuina, Zoro asked for it from her father, who then gave the sword to him.
Either a) by the same logic Shusui is technically a grade weaker than Enma, Zoro would still have a weaker blade in Enma than Mihawk's Yoru and WB's Murakumogiri, both blackened Saijo O Wazamono swords, which should be stronger than blackening an O Wazamono sword like Enma.
Crafted by none other than the legendary swordsmith Shimotsuki Kozaburou, Enma is one of the 21 O Wazamono grade swords to exist in the world of One Piece. Kozaburou forged his sword when in Wano and to the day of his death, he remembered this blade as his greatest creation.
Wado Ichimonji is the first named sword that Roronoa Zoro carried in One Piece. It was forged by Shimotsuki Kozaburou, a person from Wano Country. This sword once belonged to Koushiro, the dojo master of Zoro from Shimotsuki village, and was meant to be inherited by Kuina, his daughter.
Dressrosa Arc
After he saw it, Kin'emon became determined to challenge Zoro so the sword could be returned to Wano Country. While at a restaurant in Acacia, Shusui was stolen by a dwarf named Wicca. Zoro caught the dwarf and reclaimed his sword.
Ship(s): Oro Jackson.
In the manga, it showed he lost it by throwing the little blade of Mihawk, like he did for the cursed sword, but he wasn't ready for even the tiny little knife and he loses his eye.
Ryuma was well-regarded in Wano Country for his immense mastery of swordsmanship. At some point in time after his death, he came to be known as the "Sword God" (刀神様, Tōjin-sama?) in Wano, with his skills continuing to be regarded as legendary even centuries after his death.
Enma is the strongest blade that Zoro owns at the moment. It's one of the 21 Great Grade swords, with the potential to become as strong as one of the twelve Legendary Grade swords. Zoro accepts the challenge and takes Enma, hoping to turn it into a black blade.
According to Onimaru, Ryuma had many legends and through countless fights, he blackened his blade. While he had many legends, he came to be known worldwide for slaying a dragon in a single strike over the Flower Capital. This feat immortalized him and, after he died, he came to be worshipped as the God of the Blade.
The Muramasa is a Japanese Katana sword known as cursed and demonic. It is a real historical sword surrounded by terrifying legends and stories.
Yubashiri was one of the 50 Skillful Grade swords. Roronoa Zoro obtained this sword for free from Ipponmatsu. The sword was a family heirloom and the best sword in the shop in Loguetown. Ipponmatsu gave it to Zoro after he saw the skill and courage that Zoro showed in testing the curse of Sandai Kitetsu.
Roronoa Zoro had 5 swords throughout the series with one getting destroyed later on in the series. He was the first crew member that Luffy recruited. He was famously known as 'Pirate Hunter Zoro' as his profession before becoming a part of the Straw Hats crew was that of a bounty hunter.
Zoro originally received the Wado Ichjimonji from Koshiro. Initially, this sword was supposed to be passed down to Kuina, a girl at Zoro's dojo who defeated him 2001 times. Due to her untimely death, Zoro took possession of the Wado Ichimonji instead.