One idea could be Marinette being forced into the League of Assassins against her will. She could use her skills from being Ladybug, like her agility and strategic thinking, to try and outwit the assassins while also trying to find a way to escape. Another plot could involve her having to team up with some of the assassins to take down a greater evil that threatens both the League and her home. Maybe she has to use her creativity to modify the League's weapons or fighting styles to defeat this new foe.
Marinette might start off as a scared and confused character when she first enters the League of Assassins. But as time passes, she would become more determined to survive. She would gradually learn the ways of the assassins and use her own unique skills to her advantage. Her development could also involve her becoming more assertive and confident in her abilities.
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.
A possible plot could be that a powerful artifact is stolen and both Marinette and Peter Parker are separately investigating it. They cross paths and initially suspect each other. But as they start to share information, they realize they are on the same side. Marinette's kwami could also interact with Peter in a really fun way, like giving him some extra powers for a short time. This would lead to some comical and action - packed scenes.
One possible plot could be that Naruto is secretly recruited by the League of Assassins. He initially joins thinking he can change them from within but soon realizes the depth of their dark and violent ways. He then has to use his ninja skills and his unwavering belief in friendship and justice to either reform or escape from the league.
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 idea could be that they face challenges in their superhero lives while being pregnant. For example, they have to keep their identities secret even more carefully to protect their unborn child. Another could be that they discover new powers related to the pregnancy, like a connection between the baby and the Miraculous.
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.
Here are some plot ideas. Felix and Marinette could be paired up for a dance competition at school. At first, they are both reluctant, but as they practice, they develop feelings for each other. Another idea is that there's a new villain in town who targets Marinette specifically because of her connection to the Miraculous. Felix, being the observant person he is, notices the strange things happening around Marinette and decides to help her. He might even pretend to be her bodyguard. And finally, a story where Felix and Marinette accidentally swap bodies due to a magical mishap. They have to figure out how to reverse it while also dealing with each other's lives and responsibilities.
Maybe their child gets sent back in time to when Adrien and Marinette were still just friends and classmates. The child then has to figure out a way to get back to their own time without changing the past too much. They might accidentally cause some comical misunderstandings between their parents - to - be in the process.