But in BOTW this goes in reverse. It's a demon trying to become a man then when defeated turns back into a demon again.
In the tapestry, Ganon is shown attacking as a demonic form, nowhere in that tale is he mentioned to show up as a Gerudo/human, he is only mentioned as Calamity Ganon. I know the Gerudo say he came from them, and I think it's somewhat touched on in the King's diary, but I found it strange that in the time before the First Great Calamity, that he didn't try to rebuild/reincarnate/whatever before that and show up as that, when there possibly couldn't have been any excuse to either being restrained by Zelda or contained under the castle.
Even when he's contained under the castle, he doesn't appear to have built any kind of body. While at first this could be ascribed to the Ancient Shiekah monitoring his containment chamber and preventing such a thing, after the King forbid them from using any of their technology, there wouldn't have been anyone after that to keep an eye on him. Even if there had been some magical field to prevent him from doing this, evidently whatever got placed weakened or wasn't good enough, and did not prevent him from breaking free. With any possible field, there would have been a prior time where it still 'worked' but wasn't as good as it used to be, and during that weakening period he could have gradually begun to rebuild a body under the Royals' noses, even if it was tiny bit by tiny bit, but he didn't.
The only time he seems to try to make a body is when he is restrained by Zelda in the castle. Either this is planned, or it is a response to being restrained by Zelda in the castle. Before and after this body is destroyed, and as he is trying to escape Zelda's sealing magic, he floats about as a giant boar-shaped Malice cloud. When he takes a form to fight Link on horseback, he doesn't take the form of a giant man composed of Malice, he takes the form of a giant demon boar, and it is composed in mere seconds rather then taking a century to build like the body inside the cocoon.
The other thing about this body is that it is messy with extra legs and arms and is spider-shaped. It is not very human-shaped besides the head, and the head itself looks like it is melting or half rotted. This can't be ascribed to being dimwitted or too 'feral' to know what a human body is supposed to look like, as his Blight Ganons have mostly human shaped proportions and bodies and don't look like spiders or giant pigs. Even with the additions of the Blights to his physical form, he never uses them to merely add mass, strength and power to any existing human-shaped arms, legs, or torso (using the head plates and other things as body armor) he just emerges as a giant spider.
As a last part, even as Zelda says in the Japanese translation that he hasn't given up on reincarnation, it doesn't seem like he has put much effort into it either. Either a human form is a distant rainy day project for him or he does not care about reincarnation into a human form, and his idea of 'reincarnation' will be something different in mind.
So any flaws with this observation? This Ganon 'behaves' somewhat differently then the prior games he's been in, and I am wondering if there might be any 'clues' as to what the devs might be taking him in the next games, since I think they've said that continuity might be a bit higher priority now. He will have to be a plausible and versatile end boss to face in future open world Zeldas, and will need ways to keep him interesting and full of surprises.
Rymes with 'Achoo.'