A possible plot idea is that Marinette is akumatized after being wrongly accused of something at school. Her akumatized form could have the power to manipulate people's memories, making them believe false things about their friends. This would cause a lot of chaos and mistrust in Paris. Chat Noir would have to find a way to reach the real Marinette inside the akumatized shell and convince her to break free. It would be a story full of drama and action.
Well, perhaps in the fanfiction, Marinette is akumatized due to the pressure of keeping her identity a secret. She might start to feel isolated and that no one really understands her. Her akumatized form could have powers related to secrecy and shadows. She could create illusions to deceive those around her, especially Ladybug's enemies who are trying to find out her true identity. And she might also use her powers to manipulate the memories of those who get too close to the truth.
One plot idea could be that Marinette and Felix are paired up for a school project. Felix, initially cold, starts to see Marinette's kindness and creativity, and they develop an unexpected friendship. This could lead to some comical moments as Marinette tries to hide her Ladybug identity from him while Felix is being his usual perceptive self.
One plot idea could be Marinette having to deal with the pressures of being a princess while also being Ladybug. For example, she might have to attend royal balls and diplomatic events in her princess role, all while secretly protecting Paris as Ladybug. Another idea is that an evil villain targets her specifically because of her dual identity, trying to take over both the kingdom and Paris. Maybe there could also be a plot where she has to choose between her duties as a princess and her responsibilities as Ladybug, creating an internal conflict.
One interesting plot could be Felix discovers Marinette's secret identity as Ladybug by accident. He then has to decide whether to use this information for his own gain or keep it a secret. Maybe he starts to develop feelings for her because of her dual identity and the strength she shows as Ladybug.
She could be turned into a mouse - like creature by an experimental akuma attack. As a mouse, she discovers new parts of Paris that are usually hidden from humans. This could include secret underground tunnels or the rooftops in a whole new perspective. She might also meet other kwamis who are more active in these hidden areas.
Well, a fanfiction about Luka getting akumatized might start with a misunderstanding. Maybe he sees Marinette and Adrien together and misinterprets their relationship. As an akumatized character, he could have a really cool and menacing design. His akuma form might be named something like 'Melodic Mayhem' and his powers could involve disrupting the harmony around him, not just in a musical sense but also in people's relationships. This would force Ladybug and Chat Noir to think differently when fighting him.
One interesting plot could be that Marinette - as - Kwami is accidentally discovered by Hawk Moth. He tries to capture her to use her powers for his evil plans. Marinette then has to use her wits and any new Kwami - like abilities she has to escape and warn Ladybug (who she can't transform into at the moment). This would create a lot of tension and action in the fanfiction. Also, it could explore how Marinette feels being in such a vulnerable state.
One idea could be that Marinette vomits due to extreme stress. Maybe she's facing too many akuma attacks in a short time and the pressure gets to her physically. Another could be related to a strange side - effect of using the Ladybug Miraculous. For example, if she overuses her powers in a short period, it might cause some sort of physical reaction like vomiting.
A possible plot is that Adrien is akumatized after his father is extremely harsh on him for not following the family's strict rules. His akuma form, 'Rebel Son', might have a look that combines his Chat Noir features with a more rebellious and angry look. Marinette could be akumatized when she's framed for something she didn't do at school. Her akuma form, 'Innocent Victim', would have a look of someone who has been wronged and is out for revenge.
One idea could be exploring how Marinette balances her superhero duties with her pregnancy. Maybe she has to be more cautious during battles, and her partner Chat Noir has to be extra protective. Another plot could involve her friends and family finding out. Some might be overjoyed while others could be worried about how she'll handle it all.