Roronoa Zoro was one of the best swordsmen in anime, even in the early stages of One Piece.
His Three Swords Style style attracted fans, making him an instant favorite. However, there are some inconsistencies with his abilities in the One Piece anime version, especially in the Alabasta arc.
In the battle with Daz Bonez or Mr. 1 by Baroque Works, Zoro struggled to win against the devil fruit eater Supa Supa no Mi. This Devil Fruit allows the user to transform part of their body into a steel blade, causing Mr. 1 becomes the perfect rival to Zoro.
The battle with Daz Bones was arguably the most difficult and life-changing that Zoro faced before the timeskip. It taught him how to cut steel, giving him the upgrade he needed if he wanted to become the strongest Swordsman in the world.
However, a filler episode of One Piece proved that this match should not have lasted even a minute. Because this filler episode showed Zoro cutting through a giant steel chain without breaking a sweat. So why did he struggle so much with Daz Bonez?
Zoro had never been able to cut steel before fighting Daz Bonez
In episode 59 of the anime, we see Zoro severing a bulky steel chain. This is actually a filler episode produced by Toei Animation to prolong the anime. This episode caused great confusion regarding Zoro's abilities and made his fight with Daz Bonez inconsistent with the abilities anime fans had seen him perform.
The blue-haired swordsman of the Straw Hats had never been able to cut through steel until his fight with Mr. 1 forced him to face this head-on. In the One Piece world, Mr. 1 is certainly not the only one who can turn into steel and Zoro will have to face others just like him. Zoro did not give up on this battle, despite how difficult it was.
At the climax of the match, Zoro turned the situation around when he “experimented” with the power to cut Mr. 1's iron body.
This battle is where Zoro unlocks the strange ability called “the breath of all things”. He can hear inanimate objects and cut through them. This is an unexplained power but from what we can understand, it is a balance between Armament Haki and Observation Haki for swordsmen.