Roronoa Zoro, also known as the Pirate Hunter Zoro, learned the formidable power, known as Haki in the time skip of the series. The time skip in the One Piece series comes in between chapters 597-598 in the manga and in between episodes 516-517 in the anime adaptation of this popular series.
Disclaimer: This article will contain information revolving around Zoro and might contain spoilers for some audiences. Readers are advised to proceed at their own discretion.
In the One Piece series, the time skip refers to the two years that the Straw Hat Pirates spent separated while training in their respective crafts on different islands. The time skip occurred after the war at Marine Ford, known as the Paramount War. Luffy, Zoro, and the rest of the crew separately spent two years training to prepare themselves for the New World.
Although the One Piece world is filled with strange and intriguing prowess and fighting abilities, Haki is undoubtedly one of the most potent and impressive powers. Kaido, an Emperor of the Sea and the Strongest Creature Alive, stated that Haki is the true power and it surpasses devil fruit abilities. After the Marine Ford War, Zoro spent these 2 years training on the Kuraigana Island under the tutelage of Dracule “Hawk Eyes” Mihawk, also known as the greatest swordsman in the world and learned how to utilize Haki.
In these 2 years under Mihawk’s tutelage, Zoro learned how to use Armament Haki and how to imbue haki in other objects to make them stronger quite well. There are also hints available that Zoro is able to use the Color of Observation Haki as well but there is not much emphasis on that. Zoro is a swordsman and the Color of Armament Haki is a way to enhance his abilities exponentially.
As long as Zoro uses his Haki well, there is nothing that he can’t cut. In the Wano Arc, it was stated that the legendary black swords got their black appearance after they were infused with Armament Haki in countless battles. It goes to show how much important Armament Haki is for a swordsman.
In the Wano Arc, there were also hints that Zoro possesses Conqueror Haki but is unaware of it. The first instance is when Zoro first met Kiku. Urashima, the sumo wrestler who was pursuing Kiku backed off after being intimidated by Zoro’s spirit. The further instances were during their raid at Onigashima.
On multiple occasions, Zoro knocked people out without doing anything. There were some individuals who wondered if it was the Color of Supreme King Haki but it was not confirmed. Nonetheless, considering the data available and Zoro’s personality, there is a decent chance that Zoro possesses Conqueror Haki, which would make him one of the few individuals who possess all three kinds of Haki.
A. Dracule “Hawk Eyes” Mihawk, also known as the greatest swordsman in the world taught Pirate Hunter Zoro how to use haki. During the time skip, Zoro spent two years on Kuraigana Island under Hawk Eyes’s tutelage.
A. Although there are signs that he may have used Haki much earlier, Zoro officially used Haki for the first time in episode 719 of the One Piece anime with the title, A Decisive Battle in Midair - Zoro's New Special Secret Technique Blasts!