The Princess Has a Solitary Nature

I found myself reincarnated in a game where, no matter which ending you reach, the final boss kills you in the end. "Has no one told you? When you lie, here and here tremble." I was sure my life was over… But then… “But from now on, I wish this would turn into a secret affair.” “A late warning, but you should’ve been careful from the start. Once you give someone like me permission, there’s no turning back.” "Final Boss, why are you acting like this all of a sudden?!" (Source: MangaUpdates, edited)