i wanna mention some note that may expand the perspective a bit further.
- we know that shimotsuki kozaboro the master sword-smith that forged enma, was believed to have broken the law and left the country with a number of people from his clan, what if the crime he committed was that he doesn't worship the common god of wano, aka "ryuma", but instead he chosed to worship another entity, which i think it was "enma".
after yasui's execution zoro and hiyori escaped into the forest of hakumai where they hid in a shrine named "enma shrine"
now why would anyone build a shrine for a mere sword, unless the sword wasn't the subject of worship, but rather the god of hell which the sword is named after.
so maybe kozaboro and some of his clan formed a secret cult that worshiped enma, which might have been forbidden in wano, and they got exposed 50 years ago, and so they were banished from wano country.
kozaboro may not have told zoro that the shimotsuki clan are from wano, but he did share some of the culture with him, like the word "sunachi"
also in zoro vs mr 1, in the flash back we saw that zoro came very excited to tell his sensei of what he heard, it looked like he just heard it from some one, and i think that someone was shimotsuki kozaboro
so it's very possible that kozaboro would sit zoro by his side and tutor him in philosophical/religious concepts and how they influence swordsmanship, asura might be something that zoro learned from him.
There's an Instagram post on this with the title "Zoro and 6 realms of Buddhist Cosmology" that associates Zoro's abilities with 6 realms of Bhuddist cosmology especially Ashura. Check it out its interesting.
i think three kind of haki (coc,coo and coa) are a classification to learn the basic use of haki (the same in maths when the kids learned addition and substraction) but when you have more level you know than substration is addition with negative number so the haki is the same coa is "adv coc" but there isn't (or is a bit) ambition