Sokutaijou Shitai Wakiyaku nanoni, Netotteshimatta Oujisama ga Nigashite Kuremasen

"You slept with me, and you think you can just say sorry and get away with it?" Estelle is reincarnated as a minor character in a popular web novel. Estelle's role in the novel is to seduce the second prince and make him dump his fiancee the heroine, and she will be condemned to exile for it. Hoping to escape that storyline, Estelle plans to just "pretend" to sleep with him during that part of the novel, but... she mistakenly sleeps with the hero, the first prince Oscar, instead, and ends up in an even bigger mess...! A doting fantasy between a minor character and the possessive, perfect prince! (Source: ZeroSum Online, translated)