In the world of One Piece, there are many artifacts like swords or Haki-infused weapons. However, only a few have caught viewers' attention and are talked about. One of them is Roronoa Zoro’s famous katana called Enma. Fans have long speculated whether Enma is actually a black blade. What does it mean if it becomes one?
Currently, no, Enma is not a black blade. Although fans have been actively speculating that it might become one. During the Wano Arc, Sukiyaki revealed that if Zoro is successful in taming his sword, it has the potential to evolve into a black blade.
In One Piece, Enma is among the 21 Great Grade Swords. It is regarded as an upper-tier weapon. Importantly, it is crafted by Shimotsuki Kouzaburou, and the first owner is Kouzuki Oden. Following Oden's death, the sword was maintained in the safe possession of his clan and ultimately was left to his daughter Hiyori.
She gifted Zoro this sword in exchange for returning Shusui, the national treasure of Wano. Enma is particularly very hard to control and master because of its peculiar trait. It forcibly draws out its wielder’s Armament Haki (Ryuo). This might sound intimidating, but Zoro took it as a challenge and worked towards taming it.

Furthermore, Enma is not just a simple sword. Its presence is a testament to the Kozuki Clan and the relationship between Oden and Zoro. Interestingly, Zoro himself could be related to Wano by way of the Shimotsuki family. Shimotsuki Kouzaburou, who forged both Enma and Wado Ichimonji, abandoned Wano and made a new home for himself in the East Blue, where Zoro was born.
Interestingly, Eiichiro Oda has named this sword Enma on purpose. The name is kept after the Japanese King of Hell. As this sword demands strength and greatness. It is a metaphor; the sword exposes how much strength its wielder truly has inside. And in mastering it, Zoro isn’t just gaining control of a weapon; he’s proving that he is worthy of his dream.
This particular sword in One Piece is so strong that it is often described as a sword that cuts to the bottom of hell. It has been so powerful that when Oden was wielding it, Enma actually managed to injure Kaidou, one of the Four Emperors. That accomplishment alone testifies to the sword's potential.
Finally, creating a Black Blade is seen as a legendary feat in One Piece. When Zoro manages to evolve his Enma, it will be proof of his achievement as he will be in complete harmony with his weapon.
Will Enma in One Piece become a Black Blade? Speculations explored

If the hints spotted by viewers add up, then Enma becoming a Black Blade is inevitable. Because it is the most logical level up for Zoro in One Piece. Zoro has already mastered the blade’s wild Haki drain. He has awakened Conqueror’s Haki and can now coat his attacks, and he’s matched legendary feats like scarring Kaidou and defeating King.
Finally, turning Enma into a Kokuto might also be a callback to Ryuma, Wano’s greatest samurai, who wielded the black blade Shusui. Zoro may be on the same path, and this could be the final step that leads him to the highly anticipated confrontation between him and Mihawk.
In conclusion, while Enma is among the strongest swords in One Piece, it has not yet become a black blade. There is a possibility for it to evolve, under the condition that Zoro masters the sword. It is a blade with its own soul, and in this story has tested his resolve. Maybe through Enma, Zoro can finally achieve his dream of becoming the strongest swordsman in the world after surpassing Mihawk.