The main arc for the “Year of Sanji” was Whole Cake Island and the relevant Yonko was Big Mom – a woman in a land which had the theme of food. Women and food, two of the most central things about Sanji’s character.
His biggest feat so far has been making the most delicious wedding cake known to man.
The next arc after the Reverie will be Wano. Relevant Yonko will be Kaido – the strongest creature in the world whom nobody has yet been able to cut. A land with the theme of Japan centralized around the samurai culture where honor and swordsmanship is fundamental.
I think most people agree that this arc will probably yield some pretty major development for our favorite Marimo. If Zoro came from a country in our world it would be Japan. He strives to become the strongest swordsman in the World, he has been compared to a demon and the only time he allowed his honour to be questioned was with Mihawk as a result of his conviction to Luffy. He wields cursed blades which he has managed to gain control over and a lot of focus has been put on what materials he is able to cut.
My guess: Zoro WILL manage to cut/graze Kaido with his blades in Wano. This would be his ultimate feat so far in terms of showing what he accomplished with Mihawk and it would truly show his growth. Of course he will get some kind of sword fight as well but this is not a unique way of displaying his growth! Sanji’s feat was different from just a regular battle, he made the cake as the chef he is. Yes, Zoro is a swordsman, a fighter, and of course a battle is central for his development towards his goal, but what he manages to cut is equally important. It has been emphasized before and should be addressed again. Examples:
– from the beginning he couldn’t cut the cage which Buggy locked Luffy in;
– cut Daz Bones;
– cut cannonballs;
– cut the tower of justice and through giraffe Tekkai;
– cut an entire ship post timeskip ;
– cut Pika (apparently strong haki, but larger feat is that he cut stone equivalent to a small mountain).
I believe the Kaido fight will consist of the 11 Supernovas vs Kaido and Zoro will manage to scratch him in some shape or form.
*Theory by AdrianoC