Both FL and ML are assassins and hide their identity in the first part of their marriage. They both work for the same organization and FL is tasked with killing ML which she thinks the easiest way to accomplish is to marry him and thereby entering his mansion. It is also a romance since the two of them fall in love with each other.

Both MLs travels in different books (Serendipity) or dimensions (The King) and finds love at some point. Both shows have a happy ending after thinking they lost each other forever.