Some Things i randomly Think of

MHA x Demon Slayer

So, this an Idea how you can merge These two Verses.

We know how Demons have Blood Demon Arts, which are basically Quirks for Demons except that they aren't Born with them. So what if some Demon with a BDA that had something to do with Light r@ped a Female or had consetual Intercourse with her and out came the Child with the Ability to make his Body glow (idk how that Quirk really Works) and over time, everyone had a Quirk and where passing those down to their Kids. And some Quirks are actually similar to BDAs. As an example, Nezukos and Endeavours Powers are pretty similar and so are Rei Todorokis and Doumas.
Animal Quirks, like Tsuyu Asuis come from Demons Like Rui who had a BDA that gave them Powers from an Animal.
Sentient Quirks like Dark Shadow (Tokoyamis Quirk) come from BDAs like Kokushibos Moon Blades, where the User can't really control the Things that come from their BDA. We could also assume that not only their BDAs but also some Traits of that Demon get passed down, Like Gyokkos Diamond Scales

Now, lets look at few Characters that could be Descendants of a Demon (im only listing Demons and MHA Characters that we know the Name of):

Denki Kaminari could be a Descendant of Kaigaku

Kirishima could be a Descendant of Gyokko

Best Jeanist could be a Descendant of Rui

Snipe could be a Descendant of the Former Lowermoon 2 (the one that Rengoku killed to become a Hashira)

Rei Todoroki could be a Descendant of Douma

Endeavour could be a Descendant of Nezuko

Vlad King could literally be a Descendant of any Demon

Feel free to give some Examples yourself