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.
Well, this kind of fanfiction could start with Marinette making a mistake while using the Miraculous. Then she finds herself in the form of a Kwami. She might be really tiny and have to find ways to get around. She could hitch rides on people's shoulders or use her small size to her advantage when it comes to spying on Hawk Moth. And she would definitely have to deal with the fact that she can't just transform back into her normal self right away, leading to all sorts of comical and tense situations.
In a Kwami swap fanfiction, a possible plot is that the swapped powers start to have unforeseen side effects on the holders' daily lives. Ladybug, for instance, might find it difficult to balance her normal life with the new Kwami - influenced powers. Chat Noir could be in a similar situation. As they struggle to deal with these changes, they also have to figure out how to reverse the Kwami swap. Meanwhile, the city is in more danger than ever as they are not at their full potential, and this could lead to some intense and exciting battles and rescue scenes.
One interesting idea could be the different powers and personalities that come to the fore when the kwamis switch. For example, if Tikki and Plagg switched, Ladybug might become more mischievous and Cat Noir more rule - abiding in a very different way. It could also lead to new dynamics in the battles against villains as the heroes have to adapt to their new powers and instincts.
Maybe the Wolf Kwami has a special power that is different from the other Kwamis. A new villain wants to steal this power for their own evil plans. The story could focus on Ladybug and Chat Noir protecting the Wolf Kwami and its power. This would involve a lot of action and adventure scenes.
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.
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.
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.
A possible plot could involve the Dragon Kwami falling ill. In the Miraculous world, this is a big problem as the Kwamis are essential. Ladybug and Chat Noir team up with other Miraculous holders. They have to search for a special cure that exists in an ancient, hidden place. Along the way, they face many challenges and learn more about the Dragon Kwami's origin.