I have mixed feelings about this.
- Zoro already had Enma has training tool, which also has Oden's haki presence within it. First powerup ("gotta release this Enma a bit more" = incomplete powerup)
- Zoro also had mid-fight, basic CoC bloom when using all his remaining strength against Kaidou in Asura's Farce of The Dead
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So he has already obtained two powerful powerups.
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My view about this
A. About Enma:
- imo this should be Zoro's main powerup focus. Since he is the CoA specialist, him taming Enma should be emphasized internally imo. If Kaidou and BM wanna tease about Oden's presence, there should be flashback about Zoro's Enma training before the raid, showing the spiritual meeting, clash and finally "compromise" and incorporation/merging between Zoro's CoA and Oden's spiritual CoA whatever, inside of Enma.
- It will explore the notion of Zoro being able to "coerce and absorb" curses and other CoAs using his own CoA, an extremely unique ability of CoA specialist, resulting in Enma being tamed completely by Zoro. If this is executed properly, this powerup alone is enough to beat King as Oden is the first to scar Kaidou and Zoro is the second. And even more importantly, it will mean so much more to the narrative: Zoro inherits Oden's will.
- tldr, if Oda explored the feel and technical aspect of CoA mastery and Enma's mastery by Zoro, it will be a powerup that is enough to defeat King.
B. About CoC:
- While i'm not sure if Zoro ever have first-level no-touch CoC Coating - let alone skysplitter-level CoC Coating - in the manga, as Luffy is the CoC specialist and he is always the most powerful especially in CoC department, but awakening basic CoC against WSC is already a good powerup in itself as CoC will add damage.
- Even without CoC, Zoro is already so strong. So add CoC qualities like Chinjao, Dofla or Katakuri to that strength, and beating King is assured. What matters the most imo is Zoro's ability to figure out how to use it, to the extent that other people can sense it that he can consciously control his CoC in the clash(Diamante realizing that Luffy vs Chinjao is CoC clash or everyone realizing that Luffy vs Dofla is CoC clash, implying the CoC is concentrated in the clash)