Want find a manga

I doubt anybody would be able to help but it’s worth a try, this manga wasn’t really popular and I remember miraculously stumbling upon but barely remember much content as it was one of the first mangas I read here on mangago

The gist is that it’s about a Male who crossdresses as female and enters the emporers harem of concubines, this maybe be me mixing my mangas but I think he acted as a replacement for his sister but he catches the emporers attention (and he falls in love ig). Ik all this sounds really vague and cliche/common but small details I can remember are that along the way he becomes friends with the other concubines, if I recall correctly at one point his sister(?) comes back and tries to re-replace him,

I just remembered more, the emporer is like a demon or a vampire or smth (immortal)(also I don’t think he can go in the sun) and it turns out the brother of the siblings is special (blood relation ancestry or reincarnation or smth), the emporer has someone he previously loved but she died and he’s cursed(?)

As I try to recall more keeps comming up and it’s all jumbled anyhow I would really appreciate anybody who could help I’ve been searching for hours