I want to explain what Enma was doing to Zoro, because it seems we actually get to see exactly how Zoro learns how to infuse Conqueror’s into his 3 sword style throughout the course of Onigashima. People still treat Enma itself as Zoro’s powerup, but nothing really indicates that his growth came from anywhere but himself. I won’t really be analyzing his character arc though, just laying out the simple power progression.
To start: The reason it almost seems as if Enma gave Zoro Haki of its own is because it absorbs any and all Haki leaking from the user. It does not hold it permanently, and can be taken back if you pass a certain threshold. Until that threshold is met: the more Haki Zoro used, the more Enma took from him. Which just so happens to pair perfectly with how Conqueror’s Haki normally works. That’s why holding Enma without the intention to attack is fine, and a burst of Conqueror’s Haki could undo the arm draining. However, Zoro did this unintentionally.
Here’s how he learned to do it himself:
- On the rooftop, Zoro willingly channels all of his Haki into his sword for a one-sword-style attack, but unwillingly “leaks” conquerors Haki. He apparently has been doing this for his strongest attacks quite often.
- However, Enma absorbs it for him, infusing this into the attack.
- Zoro does the same thing, only now focusing his Haki throughout all 3 swords.
- Unintentionally, Enma channels it all.
- Now, when the attack lands, Enma is able to cut Kaido. That’s why there’s a single slice mark.
- Zoro repeats the process again, only now more potent.
- Still gets channeled into Enma.
- However, by using Asura he’s able to create the sensation of “3 Enma’s”.
- He scars Kaido when the attack lands, as now he’s effectively infused 3 swords- for triple the cutting power.
- Later, as the fight with King proceeds, his normal attacks aren’t able to get through his opponents durability. The prior battles improved his Haki, but he’s still unable to pass Enma’s threshold without straining himself, so Enma keeps draining more than he’s willing.
- If he isn’t consistently outputting Conqueror’s into his right arm, he’s either put at risk or unable to damage King, and it throws him off.
- He decides to exert more than enough to coat Enma AND his 2 other swords; which his Asura attack showed he was capable of- though it takes great effort. Enma originally forced it out of him, but he wouldn’t be able to infuse it into his other swords if HE did not come to understand how to do it so quickly.
So no, it’s not leftover Haki from Oden in the sword or boosts from the curse or anything. Enma steals the user’s Haki forcefully and they have to get used to the sensation… or else. It’s unclear what exactly Asura is, but it doesn’t seem to be related to Conqueror’s itself. All it did was show that Zoro could triple the Conqueror’s Haki Enma was channeling for him in short bursts- hence why Kaido commented on it, to Zoro’s surprise. You should view the attack that scarred Kaido the same way you view Zoro’s post-king upgrade.