First things first. Its been a long time since I checked this forum, again. Now, I have the first part in this link here. My theory there states that zoro contained the demon inside of him and it resulted to asura. For those who are not yet done watching Fullmetal Alchemist, dont, read this. King Bradley was a human before becoming a homonculus, the crazy doctors injected a Philosopher's Stone inside him and after he OVERCAME the Stone he received an eye capable of seeing through anything, thus called the Ultimate Eye. Guess what, its placed on his LEFT EYE. Now another one of this is Akashi Seijuro of Kuroko no Basuke. He has two talents, first of which is the ability to draw the full potential of teammates, second is the Emperor eye. This one is slighlty different. When he was about to lose on a 1v1 with Murasakibara he had a change of personality ( like zoro not laughing anymore) and developed (another) eye. His LEFT EYE has a different color from his right eye. Its called the Emperor Eye, an eye that sees into the future. So after telling all these. Now what? Acc. to all these other animes, I can conclude that Asura might be the result of overcoming something and his left eye helps contain Asura. So any thoughts? Hope you enjoyed this one! God Bless!