In the world of One Piece, Devil Fruits are not the only powerful artifacts capable of wreaking havoc. There are 12 blades that fall into the Saijo O Wazamono, or Supreme Grade, category. These weapons are a cut above the rest and are only used by the strongest characters in One Piece.
Supreme Grade weapons are strong enough to cut through the toughest objects. Considering their power, it is obvious why Oda has limited the number to only 12, out of which only four have been revealed, but that will change as the story moves into its final phase.
8 Yoru
Yoru is the most well-known Supreme Grade weapon in One Piece. The blade is wielded by Dracule Mihawk, the strongest swordsman in the world. Yoru is an all-black blade that is longer than Mihawk. He has used it in many battles, and it is safe to assume that he used it to gain the title of the best swordsman in the world.
Yoru is suited to be held by two hands, but Mihawk has utilized it with a single hand as well. A single slash from the blade was powerful enough to slice a chunk of a massive frozen wave. Mihawk's dexterity is unparalleled when it comes to handling a sword, and he can use it to launch a scathing attack as well as deflect bullets with grace. All in all, it is the sword befitting the world's best swordsman.
7 Ace
Gol D. Roger also wielded a sword, but his skill remained unknown until the Wano Country arc. Roger's Supreme Grade weapon was called Ace. Roger was particularly fond of his sword, which is why he selected the name for his son.
Roger used the sword in many epic battles, including the one where he fought against Whitebeard. Roger's Ace was able to cancel out the incredible power of Murakumogiri and showed no signs of wear. Roger imbued Ace with Busoshoku and Haoshoku; a single attack was strong enough to send Kozuki Oden flying.
6 Shodai Kitetsu
Shodai Kitetsu is a cursed sword and one of the four confirmed Supreme Grade weapons. Like the other Kitetsu blades, Shodai Kitetsu is said to lead to its wielder's death. Due to this reason, most people do not use Kitetsu swords.
However, it is impossible to deny their power. Out of all the cursed swords, Shodai Kitetsu is the strongest. The current wielder of the blade remains unknown, but many fans have speculated that it might belong to St. Ethan Baron V. Nusjuro, the Godhead of Finance. Given the importance of the Five Elders, it does make sense for one of them to have a Supreme Grade Weapon.
5 Murakumogiri
Murakumogiri is unlike any other Supreme Grade weapon in that it does not resemble a sword. It is a nagatina, but just as durable as the other Supreme Grade weapons. It was wielded by Whitebeard, who imbued the weapon with the power of the Gura Gura no Mi.
Despite the destructive power of the Devil Fruit, Murakumogiri did not show any visible signs of damage. The weapon was also able to withstand attacks from Roger, Akainu, and various other characters. After Whitebeard's death, Murakumogiri was placed on his grave.
4 Enma (Potential)
At the moment, Enma is among the 21 O Wazamono swords, but it has the potential to become a Supreme Grade weapon. The blade was once wielded by the legendary Kozuki Oden, and currently it belongs to Roronoa Zoro.
Enma is a special sword that draws out the Haki of an individual. Oden had mastered Enma when he was young, and it was one of the two swords that he used to give Kaido a massive scar on his body. Zoro has gained a certain degree of control over Enma, but there is a long way to go before he can wield it without any side effects.
3 Gryphon (Likely)
Gryphon is a large saber that is in the possession of Shanks. Being one of the Four Emperors, it is only fair that Shanks' preferred sword is a Supreme Grade weapon. While the blade's grade hasn't been confirmed, there are several things that point toward it being a Supreme Grade weapon.
Like the other weapons in the category, Gryphon has managed to withstand powerful attacks. Another thing to keep in mind is that Shanks used to be rivals with Mihawk, and their battles were deemed legendary. A swordsman equal to Mihawk's skill will definitely have a Supreme Grade weapon.
2 Hassaikai (Likely)
Hassaikai is Kaido's weapon of choice. It is a kanabo that Kaido started to use way before he became a big-name pirate. Kaido used Hassaikai for the majority of his melee attacks. He infused it with both Haoshoku and Busoshoku Haki.
These attacks were devastating, and one well-placed move could knock out a formidable fighter like Luffy. While the weapon's grade remains unknown, Oda said it would be considered a legend if it were to be left behind.
1 Oto or Kogarashi (Likely)
Oto and Kogarashi are two swords that were wielded by Shiki. It is unclear how the legendary pirate got his hands on the swords, but it seems they were exceptional blades.
The swords remained intact even after Shiki fought the likes of Roger, Whitebeard, Garp, and Sengoku, which implies that they were crafted by a master swordsmith. While it may be unreasonable for both swords to be Supreme Grade, one of them should belong in the category.