HELP!!

I’m looking for this manga I forgot the name too. So basically, this girl gets reincarnated into a game she played as the OP hidden boss which is a school girl from the game world where she is like level 9999 and uses dark magic of some sort. The “FL” of the game mistakes her as the reincarnated demon lord because of her insane amount of magic (I think I don’t remember the reason clearly). I believe the game “FL” could only see the actual FL as a black fog of some sort and that’s where I left off. Oh right, if it’s helpful, the game “FL” kinda had a harem going on, I remember a prince being a part of it (cliche ik).

Thanks for the help!