Becoming a demon, and then immediately becoming immune to sunlight. That's not... well, it isn't common, let's just put it at that.

Shinko Yamamichi, nicknamed Kira. Your family got the Kamado-family-in-episode-1 treatment: killed by Muzan, save you, who was turned into a demon. It didn't affect you much, besides the horns. (And I should mention, your demon-izing was 500 years before the main timeline.)

You weren't hungry for flesh, either? You found that strange. Then you walked outside, and holy sh!t, you didn't burn up. What was happening?

You eventually just sucked it up and joined the Demon Slayer Corps. Of course, the occasional Slayer would come up and ask, "Why's a demon with the Demon Slayers?" To which you shrugged and walked away.

You went and did some stuff here and there, took out a demon here and there. You met people along the way, people who would either go on to sprout legendary bloodlines or become one of the Twelve Kizuki. There was one kid named Hakuji that really had spunk.

Which brings us to the Infinity Castle Arc of the main story. You know, the part of the story where every single Demon Slayer was dropped into the giant neverending demon base? Yeah, that.

You walked, here and there, found more demons here and there, killed more here and there. Until eventually, you stumbled across a peculiar guy with an unholy number of markings, like those on criminals in Edo Japan. Without even another look, you immediately knew this was Akaza, the Third Upper Moon.