@NichiYouji_ It's adapting the same novel, but with a new mangaka who's making different creative decisions. The other manga ran and got cancelled a few years ago, this is a new manga to help drive interest in the new novels.
Do we know if the new manga is gonna be handled by the same artist? I like the text of the story a lot, but tbqh I'm not really enthusiastic about Mani's art.
Cousins is kind of weird but 1.) I doubt the manga will ever get that serious about it and 2.) They weren't raised together for long enough for there to be any weird power dynamics or anything going on, so honestly whatever.