(I'm assuming youve already read or been recommended vinland saga, witch hat atelier, golden kamui, and frieren) Case study of Vanitas is a very pretty vampire story set in alt history 1800's france, mainly focusing on the two main's relationship with each other.

my monster secret is the biggest fluke of incredible character writing ive ever seen, i don't know how a mid tier premise could deliver as well as it wound up doing despite being a silly romance.