#I think Koyuki would look entirely human but she'd look a bit see-through in the sun

[nightlight-stardust-and-rain]

But what if Koyuki became a ghost, like, mere hours after her death? She was so very determined to not let her fiancé suffer another awful loss that she just noped out of heaven. She has a wonderful boy to marry and cherish, thank you very much!

Sadly she gets to him after Muzan does. At which point Hakuji is busy being driven insane by the hunger of a newly-born demon. Good thing that there's precisely sixty-seven freshly killed bodies near him!

Point is. Koyuki being with him as soon as he regains his senses (she had the very good idea to stay away from Muzan, he gave her a very bad feeling). Obviously he doesn't remember anything but I think having a living breathing reminder of his past with him would make him remember real fast. So he would still go by Hakuji I think.

Koyuki learns how to make herself solid enough to touch things after a few months or a few years, and Hakuji and her spend a very long time not letting go of each other's hands. Once she is able to touch things, being a ghost becomes much less sad. She can stay with Hakuji forever, there is literally no downside to that!

Koyuki being a ghost is also much less angsty than it sounds because now she's functionally invincible : she can't die of old age, blows and blades go through her, and she can't be poisoned since she can't eat. Really, not being able to eat is the saddest thing about being dead, but she figures that since Hakuji is unable to eat human food now it's only fair that she can't either! The vows say in sickness and in health after all.

Speaking of. They don't actually stay engaged that long. Of course, the wedding of a ghost and a demon sounds like a joke, but once Hakuji masters shapeshifting enough to make himself look human it's not that hard to find a priest who'd marry them (really the hardest part is to convince the priest to hold the ceremony when the sun's down). So they've actually been married for a long time when canon comes in!

Koyuki thinks that Hakuji's pink hair is soooo cute. She's also aware that his hair color and the snowflake of his demon art come from her, and she's super touched. She kind of regrets not being able to change clothes, she'd like to wear things blue like Hakuji's eyes!

Obviously having his memories since almost the beginning means that Hakuji faces a certain dilemna when it comes to eating. Koyuki helps him with finding a solution, and after a while they figure that Hakuji can go the scavenger route - find bodies that have been freshly killed so he doesn't need to kill - or eat horrible people, which is still murder but eh you do what you gotta do.

Koyuki and Hakuji, free from human restrictions, travel the whole country several times over. They don't fear illness or the elements anymore - they can play in the rain or in the snow and climb freezing mountains and neither of them needs to breathe so they can dive into the oceans mingling with the fish for hours. For Koyuki, who's always been so restricted by her frail body, this is nothing short of a dream come true. And she gets to spend eternity with her husband!

Koyuki manages to avoid Muzan's awareness by virtue of being able to be invisible and having no presence to speak of. Hakuji can feel her spirit like he can everyone's, but she has no smell and no mass and she is dead so if she goes invisible no one can know she's here except Hakuji.

Hakuji and Koyuki don't try to break the curse Hakuji is under because they're not aware it can be broken. They don't like Muzan at all but they don't have any other choice.... Of course Hakuji once tried to tell Koyuki that she wasn't bound to his master, so she could leave if she wanted to, but he didn't even get to finish his sentence before getting yelled at. At some point they learn of Tamayo, though, and, well.... It's a very interesting thing to learn.

Also! Koyuki being dead means that she's absolutely sturdy enough to learn Soryuu! I think she would want to learn to honor her father and also because Hakuji finds so much joy in it and she wants to share that with him. She's not much for fighting, and they both try to avoid demon slayers because those guys are just doing their job and they feel bad if Hakuji has to kill one of them (and anyway Hakuji is actually pretty low-key as far as demons go, what with being mostly a scavenger... And they move around a lot so they're pretty untraceable - all in all Hakuji is pretty much never specifically hunted by demon slayers).

They spend much of their time holding hands because even after centuries they're still ridiculously in love, and they may in fact have some separation anxiety (you can't blame them, the last time they were separated ended very badly for both of them).

They go see the fireworks every year and visit Keizo's grave often to tell him about their travels :)

Also! Just thought about this but I remember reading somewhere that Akaza's demon marks were actually related to his thief tattoos in the sense that they were marks of his crimes. But like. Are we talking murdered-67-swordsmen kind of crimes or killed-and-ate-people kind of crimes? Because if it's the latter, then it means that the marks developed over time (weird to think about) but also that in this au he might not have those marks at all since he kills. WAY LESS people than he presumably does in canon. Like he's mostly a scavenger which still falls under "eating humans" but....... Idk the point is that in this au Hakuji might have way less or different demon markings.