Zoro is the first person to join Luffy on his journey to become the Pirate King and is an incredibly loved character among the fans. He is a sword master who aims to dethrone Dracule Mihawk as the world's number one and take this position for himself to keep a promise to his best friend, Kuina. Zoro has come a long way and is currently among the strongest swordsmen in the entire world.
However, he is still not on the very top and this means that he still has to strengthen his swordsmanship with powers that he has yet to attain. Until he defeats Mihawk, Zoro is certainly going to gain new powers, however, there are some that suit him far more than others.
4 Proper Control Over Conqueror's Haki Coating
Zoro's latest power up in the Wano arc was Conqueror's Haki. He tapped into this power during his fight against King the Wildfire and was able to attain conscious control over it. He managed to coat all his swords in the Color of the Supreme King and, thanks to that, his attack powers increased several-fold.
Zoro was able to defeat King and declared himself the King of Hell. However, it must be noted that his control over the Color of the Supreme King is not refined at all. Zoro can only maintain this power for a period of a few minutes. According to him, Enma is too harsh and drains his Haku way too quickly. While Oden was able to wield Emma as if it were a feather, Zoro cannot do the same just yet. In order to become stronger, Zoro will certainly have to improve his control over the Color of the Supreme King as well as the sword that he is wielding.
3 Nine Sword Style With Conqueror's Haki Coating
When it comes to Zoro's arsenal of techniques, it goes without saying that the strongest one that he has up his sleeve is the Nine Sword Style Ashura that he has brought forth on very few occasions. The first time fans saw it was during the Enies Lobby arc when he was fighting Kaku of CP9. After tapping into this power, Zorro grew two more heads and four more arms, allowing him to wield more blades. Kaku mentioned that this seemed like a demonic manifestation from Zoro and, immediately after, he was taken down.
In Wano, Zoro manifested this form once again in the fight against Kaido. With his Nine Sword Style, Zoro unleashed Dead Man's Game on Kaido and, unbeknownst to him, managed to coat his swords in the Color of the Supreme King. This allowed him to scar Kaido. While Zoro has, technically, already coated his swords in the Color of the Supreme King while using Nine Sword Style, he did not do it consciously. In the future, Zoro will certainly have to figure out a way to do this in order to grow even stronger.
2 Enma Upgrade
Enma is a powerful sword, belonging to one of the 21 O Wazamono Grade Swords in the world of One Piece. This sword was crafted by Shimotsuki Kozaburo, a famous blacksmith in Wano. As with all blades, this blade can also be made into a black blade. In Wano, Hitetsu mentioned that eventually, this blade will increase in rank. In order for Zoro to do that, he will have to turn it into a black blade.
While fans do not know how exactly black blades are crafted, common logic dictates that it has something to do with the Color of Arms Haki. Once Zoro manages to turn this into a black blade, the rank of the sword will likely increase and it will become one of the then 13 Saijo O Wazamono Grade swords. Naturally, this would make Zoro much stronger than ever before.
1 The Ability To See The Future
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When it comes to the Color of Observation, Zoro isn't all that special. He mostly specializes in the Color of Arms and has decent control over the Color of the Supreme King. That's not to say his Color for Observation is lacking. It is certainly decent and he probably is the third best user of this ability in the crew after Sanji and Luffy. One of the many applications of the Color of Observation is the ability to see the future. Only a handful of the very strongest in the world of One Piece have the potential to do this, and even among them, those who are especially attuned to the emotions of others can master this ability.
Sanji, of the Straw Hat Pirates, is one such character who has the potential to become a master of Future Sight Color of Observation. However, Zoro might need to step up and develop at least a rudimentary form of that technique as well. This is due to the fact that Mihawk might have this power up his sleeve. Mihawk bears the moniker of Hawkeyes. Interestingly, before Oda settled with Hawkeyes, his moniker was going to be the Clairvoyant. This implies that Mihawk might have the ability to see the future and, if so, Zoro with certainly need to develop his Color of Observation to a point where he can manage to keep up against Mihawk.