Her Fake Husband, the Emperor

To refuse an arranged marriage, Princess Luna Crestfall makes a fake marriage agreement with a fisherman, Arthur Stone. Bound by The Soul-Binding Knot, they experience crises such as being forced into marriage by the Arcane Origin Sect and her brother being held hostage. They go from faking it to falling deeply in love, and ultimately join forces to overcome their predicament. Arthur Stone's true power is also gradually revealed; it seems he is not just a simple fisherman...