I remember a fan theory I read about a Hyuga woman falling in love with a Tengu style demon, which created the sharingan in her offspring. It was nicely fleshed out and everything - I was hella intrigued. I had prayed to the Naruto gods that this would eventually manifest into the story, but instead got an alien creature that gave rise to all ninjutsu. Way more lazy and overused concept reaching out into space instead of or on Earth or some otherworldly dimension connected to Earth in some way like a demon realm or something. I was hella disappointed when more and more of Shippuden was published. Kishimoto should've left the rest of the story to that fan. They seemed to have better writing than Kishimoto.
