A possible fanfiction could be that an akuma victim creates a scenario where everyone in Paris acts out the Romeo and Juliet story. Ladybug and Chat Noir have to break the spell while also dealing with their own feelings for each other that are amplified by the situation. They realize that they don't want to end up like Romeo and Juliet, so they fight harder to save the day and their relationship.
One idea could be that Marinette and Adrien are cast in a school play as Romeo and Juliet. Their real - life superhero identities start to blend with the characters they're playing, and they find themselves in situations similar to the original story. For example, there are misunderstandings between them due to the interference of Hawk Moth, just like how the feud between the Montagues and Capulets caused problems for Romeo and Juliet.