Well, a common theme is the mystery surrounding Emilie. Fanfic writers often try to solve this mystery in their own ways. For instance, they might come up with theories about where she is or what really happened to her. Love and family are also big themes. Since Emilie was part of the Agreste family, fanfictions explore the family dynamics, like how Gabriel's actions are related to his love for Emilie and how Adrien copes without his mother's presence.
Definitely Emilie. Fanfictions can give her a voice and a more in - depth personality. Gabriel is also quite a character in these stories. His motives and actions related to Emilie are often explored. We get to see different sides of him, like his desperation to bring her back. And then there's Adrien. His relationship with his mother, even in the absence of her physical presence, is a key aspect. His growth and how it's affected by Emilie's situation make him an engaging character in these fanfictions.
One great fanfiction is 'The Secrets of Gabriel Agreste'. It delves deep into his motives and the backstory that we don't often see in the show. It gives a more complex view of his character.
The fanfiction should also fit well within the world of Miraculous Ladybug. It should respect the existing lore and character relationships. If it can add new elements to the story while still feeling like it belongs in the same universe, that's a great sign of a good Gabriel Agreste fanfiction.
A time - traveler from the future could also be an interesting main villain. This character could have seen a dark future where the Miraculouses were misused and has come back to the present to destroy them all. But in his quest, he doesn't care who gets hurt, and Emma has to stop him from changing the past and future in a bad way.
Maybe Emma starts to have dreams that are actually premonitions of future akuma attacks. She then has to convince Ladybug and Chat Noir that her dreams are real without revealing too much about herself. Or, she could find a way to create her own superhero identity and team up with Ladybug and Chat Noir, but struggles with the responsibility that comes with it as she is still a young girl.
In an akumatized Ladybug fanfiction, the akuma might enhance her powers in unexpected ways. For example, her Lucky Charm could become a more powerful and unpredictable object. Her akumatized form might also have a darker and more menacing look, perhaps with a more aggressive fighting style. Writers could explore how the heroes and villains interact with this changed Ladybug.
In this 'Miraculous Ladybug Criminal Ladybug Fanfiction', there could be a lot of potential storylines. One possibility is that an external force is influencing Ladybug to commit crimes. It could be a new villain who has found a way to manipulate the Miraculous. This would create a great conflict as Ladybug has always been the symbol of good. Her friends and allies would be in shock and would have to find a way to stop her without hurting her. The story could also explore her internal struggle, as she might be aware of what she's doing but unable to stop herself.
A new villain could have a weapon that specifically targets Ladybug's powers. When she tries to use her yo - yo or her powers of creation, it backfires and causes her harm. This would force her to rely on her wits and Chat Noir more than ever. They would need to find a way to neutralize the weapon and heal Ladybug.