New idea! I think it's the Madara eating someone that put me on track lol, but, although I previously explored Kitsunedara already, I never did so in the context of canon (or, at least, a universe closer to canon)
So, let's see, what if we had Yōkai in the Naruto world, spirits and such. What if Madara was a Kitsune?
The idea, here, is that, Yōkai are known to be a thing, but they are accepted as a part of the environment and most are known to not interact directly with humans and the living in general. I thought it would be interesting if Madara's Kitsune traits didn't show up until later in life. Like that, he'd be raised in a similar context than in canon, meaning as a human shinobi. (he'd be half Kitsune, then, but it doesn't matter much)
The thing is that, Kitsune, in folklore, reach immortality by consuming souls, a thousand of them if I recall correctly, and to kill them, you need to cut their tail (the number of tails increase with the intake of souls. But, what it, in this situation, we had something weird happen, and the course of the story happens as it does, everyone seems human enough, until Hashirama pierces Madara's human heart.
I thought of how it could be, that just by killing the number of person Madara had throughout his life as a shinobi, he inadvertently absorbed those thousand of souls he needed to reach immortality.
The fact his heart was destroyed would have consequences (my brain keep repeating that this simple pump shouldn't have an impact on his psyche, but I need to repeat "shut up it's magic") that I'll explain later, but from that point on, Madara is not a great person.
He eats people now! He half hides from Hashirama (I'll explain in a later post that too) and lurks around Konoha
His eyes appear vacant most of the time, but sometimes, his Mangekyō comes to life.
Little bonus: Obito and Madara
Obito is NOT born a Kitsune, unlike Madara, but he got hit by The Boulder like in the og universe. Madara found him and healed him, but there is a catch. He is now also a 'Kitsune' (?), and he is not thrilled about it. Madara is, he his satisfied with having a new family member :)
(I'll explain some more later, with more sketches lol)
Just a side note, Hashirama would still be around also. I just did my typical hc with him with just an added twist. I enjoy the idea that Hashirama would be believed to be born dead at first, before starting to cry and be a very alive baby, that's something I include in the canon universe as a hc of mine. It adds some drama, creates mommy issues for Hashirama (I'll go more in depth abt it eventually lol) and really goes in the way of monster to god for Hashirama's life (mirroring Madara god to monster path) at least from how he is percieved of course.
Now, take this idea, and just add the twist that Hashirama was a forest spirit and, voilà, immortal Hashirama!