Hanayome wa Veil no Shita de Fukushuu o Chikau

https://mechacomic.jp/books/245445 The Bride Vows Revenge Beneath Her Veil summary: Mina Ise takes a job as a wedding planner at Suien Resort, aiming to get close to the founding family and uncover the truth behind her mother's disappearance. She is assigned to plan the engagement ceremony for Kazuharu, the resort's heir—but through an unexpected turn of events, she ends up entering into a contract marriage with him herself...!? How will Mina react to Kazuharu, who treats her with kindness, completely unaware of her quest for revenge?