Imouto ni Konyakusha wo Ryakudatsusareta no de, Koushaku-ke na Kouhai to Gisou Kon'yaku shitara Naze ka Dekiaisareteimasu.

One day, Anastasia's parents break off her engagement. The engagement party that was supposed to be held on her birthday is suddenly turned into an engagement party for her sister Laura and her fiancé Nikolai. Of course, she has to attend the party herself... Anastasia is humiliated and shocked when Luis, a junior student, proposes a "fake engagement" to her...? "Let's give them a shock," he laughs, and Ana, no longer afraid of anything after her broken engagement and the pity she feels from others, becomes desperate and plans to crash the engagement party to announce the engagement.