Marriage Royale's story revolves around the male protagonist, a high school student named Tsukasa Hinomoto, 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. Beautiful girls from all over Japan will come together at a school built especially for this 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.

The world as we know it was suddenly altered forever when the door for the dimension of the gods and the door of the dimension of the demons suddenly opened up. Ten years later, a boy named Tsuchimi Rin was entrusted with two princesses from those dimensions. Will he be able to keep his sanity while living with his childhood friend Kaede, trying to live a normal school life, and also being a neighbor to both of princesses and their fathers, the mighty dimension Lords? The hearts of those girls are at stake and only Rin has the key to unlock them.