I suddenly want to read a transmigration/isekai, rebirth, or Quick transmigration, into a book, game, rebirth to the ancient era, etc, in which the MC knew the story or background beforehand. BUT. I want to know if there is a novel where the MC actually find the world they transmigrated/rebirthed at is somehow different. Either the plot/history that was mentioned in the MC's knowledge actually has HIDDEN and a different reality altogether, or the characters mentioned in the plot are actually not what they are in reality. Something like, the Passerby B actually is a hidden Boss, good buddies C actually is a traitor, naive Supporting Female actually is a green tea, The heroic protagonist actually is just a pawn for other Hidden Boss, etc. Oh, hopefully, there's no Harem.
In It's better to be the Empress Dowager the fmc finds a book that tells her of her future demise in the palace harem fight. But... Spoiler: spoiler ...the novel is just the official recorded history of timeline no. 1 and her current timeline isn't set in stone because of the book/fate/etc. This might not be what you're looking for, but I'll recommend it anyway.
Ex Rank Supporting Role’s Replay in a Prestigious School MC transmigrates into a game that's considered a failure. Spoiler: spoiler He played the game untill the end, but he discovers that some random characters (that originaly die in the game for most) actually are super important. The Novel’s Extra MC transmigrates in his own book but he never finished writting it and some events were even changed/added Trash of the Count’s Family MC hasn't read all the tomes I Don’t Want This Reincarnation (BL) It's kinda harem because a lot of guys fall for MC but there's a main ML so MC doesn't engage in a relationship with more than one person at the same time Spoiler the book MC read (iirc) wasn't all there is to the world he transmigrates in.
Oh! This actually hook my interest. Thanks! Ex rank is something that fits what I want to read, awesome! Novels extra I've read several chapters and the MC is not my liking so, uh, ToCF, i've read this masterpiece of course, lol! Thanks anyway. Don't wanna this reincarnation, I've been abstaining from BL recently, but i'll put it in my consideration, haha