Ahhh I love Basara!!
Saver is similar. I like Basara more, but Saver is still pretty good.
https://www.mangago.zone/read-manga/saver/
Red River doesn't have the falling for your enemy trope, but it is an otome isekai. I remember liking the story but it's been a long time since I finished it.
https://www.mangago.zone/read-manga/anatolia_story/
I also recall this shoujo anime from a long time ago where the female mc falls for the antagonist. It was aired when otome isekai was at peak popularity and I recall the mc having some special powers. Idk if she was a priestess or what. If I find it, I'll share.
does anyone have some story recs like basara where the main characters fall in love while being unaware that they’re mortal enemies