I was about to mention Umineko, I mean, there is even a character named Knox, and it is not a coincidence. As for what it is, it is strongly inspired by Agatha

I was about to mention Umineko, I mean, there is even a character named Knox, and it is not a coincidence. As for what it is, it is strongly inspired by Agatha Christie's "And Then There Were None" but it ends up questioning the nature of reality. There is an anime but it doesn't do the visual novel justice. I don't consider the adaptation that bad, it is just that the story is so twisted and complex that it is simply impossible to fit into 26 episodes.