Marriage Royale's story revolves around the male protagonist, a high school student named Hinomoto Tsukasa, who is told one day by his parents that he was adopted. Furthermore, they tell him that his real father is a manager of a large company, meaning he is very rich and holds a lot of power. Tsukasa's real father wants his son to marry a good woman, so he sets up an event known as Marriage Royale where beautiful girls from all over Japan will come together at a school built especially for the event and vie to become Tsukasa's fiancé. The school is located on an isolated island near Japan, and Tsukasa himself is taken there to live in a mansion in the care of two twin maids: Miku, the elder sister, and Miu, the younger sister.
There are various paths the player can take in the game beyond the main marriage path provided that the player fulfills the correct requirements to open those paths up. These paths are designated by different colors and include a red route which involves investigating dangerous ruins and a yellow route which involves the girls aiming to be idols.