Yandere Headcanons 👺Demon Slayer edition👺

Yandere Spider Demon Family (platonic)

All Rui wanted was to fill that void of not having a family, he wanted that bond that he believed he hadn't gotten with his first family and that's just what he had created for himself. With the assistance of Master Muzan's blood, he was more then capable of bringing forth his vision of a family, his family. Albeit, his family wasn't necessarily "real" but that didn't hinder Rui from going along with his own delusions. After all, if he wanted a family then that's just what he was going to get, no matter how many disappointing, failing 'family members' he had to go through to achieve his image.
He is going to get his perfect family at any and all costs.

Rui
-Rui would be the one to bring you into the family, of course he would, this is his family after all. He's the one who will decide whether you're fit for your role in being part of the family, critiquing anything and everything you do, no matter how small or minimal it maybe. He'll watch you closely, having the other family members watch you as well.

-Maybe you're a demon who had run off to the mountain to flee from the Demon Slayer Corps or maybe you're a demon slayer who had been sent to take out whatever demon had been inhabiting the mountain, not knowing what you would be in for. Maybe you had gotten in the way of one of your comrades to protect them and that snapped something in Rui. Or you could be just some poor soul who wandered into their territory, how foolish of you (Imagine the Spider family with a human new addition, someone so much weaker and vulnerable compared to the rest of them.). It doesn't really matter how you came to be on the mountain, in their territory, watching you're every move Rui sees just how well you'd be as part of his family, deciding your fate then and there.

-You'll be forced to be the closest to Rui, he'll keep you by his side if he has to to ensure that you two will be bonded. He will expect you to fulfill your role as whatever he gives you, holding high expectations not only for you but everyone who becomes part of the family. You won't be exempt from consequences and or punishments if you're deserving of them, but the least Rui will make an exception for is that he'll never kill you.

-You'll surely, without a doubt, give into the family fantasy. At first, you'll just be playing house to save yourself from punishment or overall death, but you'll gradually fall into your role as part of the family, probably lying to yourself to the point of believing that they really are your family.

-Rui, along with the rest of the family would probably prefer someone who is naive and kind, someone who can be easily manipulated and controlled by them. Having someone full of warmth and kindness would be a complete change compared to the cold and loneliness they all are subjected to, even within the family.

-Rui can be rather possessive and territorial of you, even with the other family members, but they've learned their places by now. Or at least some of them have. The others will just have to be taught a lesson until it's carved into their memory that your time is mostly Rui's. He sees the other family members as disposable compared to you, you're the one that really means something to him, especially given his image of family.

-He sees you as family and feels a real bond with you, unlike the 'fillers' that are your guys' other family members. Rui has no problem getting rid of them and just having it be the two of you but that would hurt you, wouldn't it? After all, you have grown to see them as family, how could you just let Rui take them away like that?

-You'll be the only one who can manage to keep Rui at bay with his outbursts and bashing out at the others. You're able to save them from their inevitable dates, even just for a time, but you can't be their savior all the time. You do have a role to fulfill as as part of the family now, and Rui will remind you of that time after time.

-Rui will have his soft moments, only with you though. The longer you prove your worth, filling your role and forming a real bond with him, he'll be more likely to allow himself to feel vulnerable with you. Something he didn't know he was capable of anymore. You'll be able to bring out the real Rui as long as you're willing to try.