This Reincarnated Countess Is Trying to Escape From Her Prince

Countess Sherazade of the Holy Kingdom of Florentino is hit with a flood of memories. Memories of a past life, in which her current life is just a teen love novel called, "The World that Surrounds Me," or "My World" for short. Her life is about to go from tragic to downright traumatic and she's not about to sit around and let it happen. In order to do that, she can never, ever marry the prince! Read This Reincarnated Countess Is Trying to Escape From Her Prince / 転生令嬢は執着王子と死亡フラグから逃れたい
The protagonist is reborn as Ruivel, a background character and princess in the fantasy novel Legend of the Hero of Light. Even though she was supposed to be a minor character, Ruivel suddenly receives a marriage proposal from the novel’s hero, Heizen. Thinking she might have changed the original story, she feels overjoyed and begins living a happy life. But one day, she catches Heizen cheating on her. That’s when she realizes this world isn’t the novel at all, but actually a terrible game based on it. In this version, she’s nothing more than one of the love interests meant to be tossed aside by Heizen. Fueled by anger and a desire for revenge, Ruivel meets Ancelot, the prince of a neighboring kingdom who is infamous as a bloodthirsty killer. “You want revenge on him, don’t you? Then use me, Princess.”