I read a webtoon where the FL is killed by the ML and returns to her childhood days. To keep herself from dying, she decides to endear herself to the ML for... some reason I can't recall. The thing is that the ML pretends to be a girl until his teen years, I think to keep from being killed off by rivals for the throne. I think he's a prince. He's a jerk and the FL lead hates and fears him in equal measures.

The most interesting part of their dynamic is the FL's legitimate hatred for the ML. There are quite a few scenes where she fantasizes about killing him in gruesome ways. One included bashing his skull in with a rock. I think the ML knows about her hatred and keeps her around out of curiosity.

Note, I'm pretty sure this isn't an isekai story. FL led a 'full' life, was executed by ML and went back in time.

I'm no angel, but I'm more pure than you.

Your Majesty, Please Spare Me This Time

Yes, this is it! Thank you~

I'm no angel, but I'm more pure than you.