Oda has been constantly utilizing the aspects of Hinduism and Buddhism this arc, all the way from power-ups, to the attack names, to the Wisdom Kings. Additionally, Zoro's kit in itself has been full of such references to the aforementioned religions, as well (Asura, most of his attacks, ISDS, etc).
Going over it, I think Zoro's next PU, after he wakes up, will be a new form based around Yamantaka and Yamraja from Hindu/Buddhism Mythology, and thus the thread.
Though, note that obviously Black Blade will happen in Wano, although I don't think it has anything to do with his current predicament and the boost he will get from waking up after potentially bypassing death.
So, first let's get over as to why Zoro represents Yamantaka both in terms of his own character, as well as the running plot-line within arc itself:
Yama (Or Yamarāja) is the deity of death and essentially the King of Hell in Hindu and Buddhist mythology.
That already goes hand-in-hand with Zoro's recent development. They both share the prospect of "King of Hell", and the theme of "God of Death" is kind of working well with Zoro in the moment, specially considering he might have to conquer death in itself to wake up.
Not only that, but "Enma" in itself is just another name for Yama.
Yama also, in a way, can be considered an upgraded phase to Asura. Yama is the supreme demonic God who rules over hell and death- meanwhile any demonic creature, generally speaking, can be referred to as Asura.
Literally everything that's been building up for Zoro this arc can be centered around elements of these elements.
Additionally, Wano has a running theme regarding the Five Wisdom Kings:
Luffy was compared to Fudō Myōō. The Wisdom King Acala, who also holds a strong resemblance with his mentor:
Meanwhile, Kaido was also referred to as a Wisdom King, however, we weren't told which one Kiku was referring to:
However, we can deduce which one Kaido represents based off of his Ragnarok attack:
"Three Worlds" can be significant in another way, as one of the Wisdom King is called the "Conqueror of Three Worlds"
This can easily parallel Kaido with the Wisdom King Gōzanze Myōō,
who's mission is "To protect the Eastern part of the world", which goes hand-in-hand with Kiku's explanation.
It's a possibility that there will be characters representing each of the Five Wisdom Kings by the end of Wano (Yamato and Momo are also strong candidates), and although I'm not sure how two of the remaining three will go, Zoro's parallel seems to be quite clear.
One of the wisdom Kings is Conqueror of Death, who directly mirrors Yama:
Yamantaka, or Daiitoku Myōō, is the nemesis of Yamaraj, who almost completely mirrors the Hell's King in every manner.
Yamantaka's name, in fact, literally translates into Destroyer of Death/Yama. It's a deity who has conquered death in itself.
This goes hand in hand with the idea of Zoro prevailing over vanquishing death (the Reaper he's seeing) and attaining enlightenment upon waking up again.
Let's also mention some less notable similarities between Zoro and Yama or Yamantaka:
- Both are often depicted in all black robes with red or golden accents. This is very similar to the outfit Oda picked for Zoro within Wano
- Their mounts are depicted as either a Buffalo or a Bull. You know where else was bull shown during this arc?
- Not only that, but currently Franky is carrying Zoro. Guess which animal Oda picked to represent Franky?
- Additionally, Zoro has some attacks themed after bulls, although this is a weak link as Zoro often has animal-themed attacks.
With everything said and done, Zoro is by far the most fit to represent this particular Wisdom King as far as the current plot-line of resemblance goes. It'd actively make less sense if he doesn't, at this point.
Now, going over what this could potentially mean as a power-up:
First of all, let's talk about this:
Here, Oda shows us how Zoro would look like at age of 40, and 60.
But the important part is the caption:
Zoro is saying "Yontoryu" (Four Sword Style) and "Gotoryu" (Five Sword Style) respectively.
While one can dismiss it as some joke, it makes very little sense for Oda to randomly throw it in, considering both are pretty damn impossible. Not to mention Gotoryu doesn't even make sense- if he was making a joke on numbers, he could've just said Rokutoryuu (60 years old Zoro using 6 swords style?).
However, looking at depictions and descriptions of Yama and Yamantaka, it can make a lot of sense:
Furthermore, from the Wikipedia:
Yamantaka is a direct mirror of Yama in every manner, too.
Four arms. This can make both Yontoryu and Gotoryu possible depending upon whether Zoro puts the last blade in his mouth, or not.
It can perhaps be a less "congested" version of Asura. With four arms and a single head, albeit unlike Asura, this one can be maintained for a long period of time.
Basically, a new form altogether, much similar to Gear 4, which Zoro can stay in during prolonged battle.
It also goes hand-in-hand with Oda's theme of "less is more", shown through Luffy's awakening (comparing it to the stacked looks of G4):
A more stable form than- if not a more stable form OF Asura, with more compact look, yet more power behind it. Perhaps with his skin turning of different color, as well?
Not to mention, that form can truly represent the Wisdon King,
Daiitoku Myōō.