Mismatched eyes like result of Demon possesion.
Demon possesion in the sense it's likely linked to Devil fruit demons or some demons which came out of rituals.
A split personality basically, Kids who were born with demon alongside them. 'Cursed'.
Manmayer grow above already says he couldn't awaken it but she can.
So Heterochromatic eyes aren't power but what you awaken out of them.
Only other person we know of heterochromatic eyes is,
Other eye color shows cursed nature of him. Hakuba basically.
Now why does Cavendish awakened it?
Connect the dots,
- World government Holyknights go around to have kids with unallied nations.
These children are special in every use case possible. Because they have blood of Ancient Celestial dragon and Maybe used for experimentation and Rituals.
- It was never confirmed how Bonney got her fruit, Saturn revealed it was out of experimentation or maybe rituals. WG was after Bonney as well.
She doesn't have the heterochromatic eyes but She has powers.
So my theory being,
- Normal eyes - Human conscious is active.
- Heterochromatic Eyes - Demon possesion and likely chances of awakening one powers as well.
- Both eyes ringed shaped - Utilising those powers. Only Imu, Mihawk are candidates for it. Some other entity powers or Personality is at play here.
- Other both ringed shaped eyes or different eyes.
- Bigmom, Abnormal since she was a kid.
- And when her hunger pangs hit. She is a completely different personality and her eyes switches to Double ringed.
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- It's speculation but Bigmom ate mother carmel and rest of the kids, and also a possiblity mother carmel soul influence her.
- Or it could simply devil fruit demon.
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- Kaidou,
- Kaidou never showed double ringed eyes until, he started using Drunken dragon mode.
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- Evidently this is the only moment where Luffy complained about Haki getting more stronger. Kaidou got stronger, faster than he already was.
- Luffy gear 5 also have different color eyes, as if something else have taken over, even Kaidou questioned that.
Now there are triggers to it, for double ringed pattern,
- Cavendish needs to sleep, for Hakuba to awaken and get Double ringed eyes.
- linlin needs to be hungry, for other personality to take over.
- Kaidou needs to ge drunk, to bring out the stronger form.
Now coming to character who have completely masterrd their demon or whatever power it is.
- Imu
- Freely uses the power without loosing his own self.
- Mihawk
- Zoro calling S~Hawk more Human compared Mihawk. No one really understood why?
- Imu and Mihawk both have powers which feels absolutely demonic.
Zoro just saw a Shikigami end of the wano, Literally representing 'King of Hell'
On top of that, Zoro left eyes is closed since pre time skip with no valid explanation towards it.
