Powers & Abilities Hiryuu Kaen: Fire, Haki, Some Combination of the Two or Something Else Entirely?

[Cinera]

Introduction
In chapter 1002, when Zoro was preparing Hiryuu Kaen we see something gather around his sword:

There seems to be no consensus on what exactly the aura we see building up around Zoro's sword is. I've written my thoughts on it elsewhere, but I thought to make a proper thread about it since the contention regularly comes up.

Below, I would try to perform a comprehensive analysis of what the mysterious aura might be, based on what we've been shown in the manga so far.


Fire
I think it's very unlikely that Hiryuu Kaen is just fire. It is shaded far too darkly to be a sword on fire.
This is how Oda draws Zoro's swords on fire:

This is how Oda draws the fire Kinemon's Foxfire technique produces:

This is how Oda draws the flames generated by Hiryuu Kaen:

In contrast the aura around Zoro's Enma is much darker:

Giving the dark near black shading, I think it's very unlikely the aura around Enma is mere fire.


Haki
I think there are reasons to believe that haki might be the source of the aura around Hiryuu Kaen.

• Before preparing the attack, we see an aura gather around Enma that is clearly not fire:
  
  
  • The mysterious aura seems like ryuo to me.
• Enma is hardened, so Zoro is clearly imbuing it with haki:
  
  
• Enma's special property is to force its wielder to release excessive amounts of ryuo:
  
  
  • Given what we know of Enma's ability, a mysterious aura building up in large amounts around Enma before a powerful attack is probably ryuo.
  • Release of large amounts of ryuo is how Enma produces large slashes.
  • Hiryuu Kaen did in fact produce a very large slash:
    
    
    • It's normally a close range attack and not a flying slash, so the excessive range was probably produced by the release of Ryuo.
• Haki/ryuo is the main auxiliary power source in One Piece, and the source of most auras, so a safe bet is that this unknown aura is probably haki.

All the above said, there are reasons to be sceptical that the aura that built up around Zoro's Enma was haki alone. It is drawn pretty differently from other instances of haki we've seen.


When haki overflowed from Zoro's swords when he blocked the Bird Cage, it was pitch black:

When haki overflowed from Zoro's swords during Rengoku Onigiri, it was pitch black:

When Zoro first used Enma, the haki that was overflowing from his sword was pitch black:

When haki overflowed from Whitebeard and Roger's weapons during their clash, it was also pitch black:

Given that all previous uses of overflowing haki were pitch black, I think it's unlikely that this is a usage of just overflowing haki and it happens to not be pitch black.


Conclusion
Based on all the information available, I think the aura that built up around Zoro's Enma was fire that had been imbued with overflowing haki (hence the near black colour). If you look closely, the shape of the flames resembles the shape of the flames produced by Kinemon's Foxfire style (how Zoro might have generated such flames in the first place):

I don't think that's just a coincidence, and we know that Zoro was using haki when he prepared the attack. Zoro's overflowing haki infused with the Foxfire flames and turned them black. so basically Amaterasu xD.


The official coloured scans would make this clear, but they would likely not reach this chapter for around 2 years (they are currently at chapter 931), so it's unlikely this would be settled anytime soon. The anime's depiction of haki has taken way too many artistic liberties to be a reliable indicator of Oda's intent here.

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[HA001]

Its clearly the spirit of oden still burning from being boiled...

 

[Blother Fertitta]

Zorohaters don’t know how to read. This is probably why Oda blesses us. Cuz we take the time to appreciate and meticulously dissect his work.

You and @Fenaker have been working overtime proving Zoro greatness.



Also in my perspective, that Zoro prep attack is similar to the Whitebeard/Roger attack as it develops an aura coating, supplemented by Big Moms fear, and Kaidos subsequent Dodge. This was a built different attack.

 

[Rivaille]

I guess is that it is fire with overflowing Haki which will be translated by blue flames.

But I think that Zoro next attack with this kind of aura will answer the question

 

[Chaves]

Blue flames. Dark blue, that's why it's more grayish

 

[trav]

its shading

 

[сука]

It's haki flames, that's why it's lighter than haki but darker than normal flames

 

[Finalbeta]

It should be haki.

This is no news that haki can generate an aura surrounding a sword basically.

 

[Chrono]

Its the will of the swordsman hes leeching off

 

[Ace]

Aesthetic

 

[сука]

Its the will of the swordsman hes leeching off

 

[Rukusho]

Looks to me like both, Zoro is looking beastly as of late.

But if his haki is leaking similar to that of Roger and & Whitebeard our Boi is growing

 

[Warchief Sanji D Goat]

That's Oden's haki.

 

[ZoroSlaysDragonTuna]

Its clearly the spirit of oden still burning from being boiled...

Poor oden

Post automatically merged: Jan 31, 2021

Probably haki if i had to take a guess, Enma will be a black blade soon

 

[Finalbeta]

That's Oden's haki.

Oden is a dead man however and haki can't be stored inside swords since black blades don't store it proven with the Monet paradox. Enma is an exception by sucking haki but it can only do that when the host is wielding it. It's momentary.

Enma is not meant to become more powerful each time it sucks Zoro's haki in fact, that would be straight up ridiculous to be honest.

 

[Robin swan]

Imo it's clearly a darker shade than fire so to me it's haki. Also zoro never just made fire so I doubt he can just summon fire.

 

[Stack Bundles Chinx]

Fire and odens haki

 

[Cinera]

Also zoro never just made fire so I doubt he can just summon fire.

Kinemon could though, and Zoro copied his technique.

 

[CbShadow]

It's flames, probably blue flames, that were darken by Zoro's haki.

I would also add Zoro used his right hand to perform the attack. He is left handed and normally uses his left hand for 1 sword style attacks.

 

[Robin swan]

Kinemon could though, and Zoro copied his technique.

True but kinemon was a fire based character. Zoro could steal his fire cutting move without stealing his ability to make fire. If zoro can just take anything a swordman does then he's gonna enter god tier in a couple arcs.