One Piece: Zoro's Asura Form, Explained

gamerant.com:

One Piece's Roronoa Zoro is the swordsman of the Straw Hat Pirates and one of the strongest fighters in the entire series. Being the second-strongest member of the crew after Luffy, Zoro is often in the midst of some of the most incredible fights and with every clash, he gets closer to his goal of replacing Mihawk as the World's Strongest Swordsman.

Roronoa Zoro has gotten incredibly powerful ever since the death of Kuina, which pushed him further to keep his promise to her and in doing so, he's attained some incredible power-ups. Not only has Zoro received power-ups in the form of some great swords but he's also developed some others such as the rare Asura that he's busted out on more than a few occasions. While every fan knows that Asura's power is incredible, a lot about it remains a mystery to the fans.

One Piece: Strongest Members Of The D. Clan

Just like the other members of the Straw Hat Pirates' Monster Trio, Roronoa Zoro played a massive role in One Piece's Enies Lobby arc to help rescue Nico Robin and save the day. Just as Luffy powered up by creating Gear Second and Gear Third to take down Lucci, and Sanji tapped into the hellish flames of Diable Jambe, Zoro tapped into the power of the demon spirit Asura. While very little is known about how and why Zoro could use this ability, there have been hints of Zoro having a demonic presence from the very beginning of the story. In Enies Lobby, fans saw this presence of his get even stronger and, at one point, Zoro's demonic aura manifested itself in physical form, surprising even his own allies.

In the fight against Kaku of the CP9, this demonic aura of his kept getting stronger and as the fight continued, it started to manifest further. Kaku felt that he got overwhelmed