One consequence could be a power imbalance in Paris. Since Ladybug's Miraculous is crucial for maintaining the balance against evil. If Cat Noir takes it, he might not be able to use it as effectively as Ladybug, leading to potential chaos as Hawkmoth could take advantage.
In a fanfiction scenario, Cat Noir taking Ladybug's Miraculous could also lead to a rift in their relationship. Ladybug might feel betrayed that he took her power without permission, and it could take a long time for them to regain trust in each other.
It could also change the entire dynamic of the story. Maybe Cat Noir taking the Miraculous would lead to a new form of power that combines the abilities of both Miraculouses. This could potentially make him a stronger hero, but it also comes with the risk of him being unable to control the new power properly.
The storyline could progress with Cat Noir initially being excited about having both Miraculouses. He might try to show off his newfound power, but quickly realizes that it's not as easy as he thought to handle both at once.
There's a fanfiction called 'The Miraculous Origins'. It delves deeper into the backstory of the Miraculous. It explores how the Miraculous were created and how they came to be in the hands of the current holders. It's a long read but worth it for fans who want to know more about the lore of the Miraculous Ladybug Cat Noir universe.
One possible plot could be that Hawkmoth manages to finally corrupt Cat Noir. He might start causing chaos in Paris, attacking Ladybug instead of helping her. Ladybug would then be in a difficult situation, having to either try to save her partner or defeat him to protect the city.
If Cat Noir steals Ladybug's Miraculous in a fanfiction, it could lead to a dark turn in the story. Maybe he's being controlled by an outside force. This would shatter the trust between them and change the whole dynamic of their fight against evil. The city would be in more danger as Ladybug is a key protector.
Well, a common fanfiction idea is to give the characters new powers or challenges. Maybe Ladybug has to deal with a new type of akuma that nullifies her usual powers. Or Cat Noir has to face an enemy alone without Ladybug's help. Also, there are fanfictions that play with the idea of the characters' identities being revealed in unexpected ways, which then leads to a whole new set of problems and solutions for them.
Definitely Tikki and Plagg. These Kwamis are essential to the Miraculous universe. Their interactions with Cat Noir and Ladybug, as well as their own little quirks and personalities, can make for really fun fanfiction. Additionally, Sabrina, Chloe's sidekick, can be an interesting character to include. She could have her own story of breaking free from Chloe's control or getting involved in the hero - villain drama in some unexpected way.
Hawk Moth could still be the main villain. He might target Tom specifically because of his relationship with Marinette (Ladybug). Maybe he thinks that by akumatizing Tom, he can get closer to getting Ladybug and Cat Noir's miraculouses.
Marinette and Adrien, as Ladybug and Cat Noir, finally decided to tie the knot. The city of Paris was filled with excitement. The wedding took place in a grand cathedral. Ladybug walked down the aisle in a beautiful white dress with red accents, while Cat Noir waited at the altar in his dashing black suit. Their kwamis were there too, Tikki and Plagg, looking on with pride. After the ceremony, they transformed briefly to soar over Paris as a newlywed superhero couple, sharing a kiss in the sky.
To write a good Miraculous Ladybug Cat Noir fanfiction, you should start with a strong concept. It could be a 'what - if' scenario, like what if Ladybug and Cat Noir's identities were revealed early. Then, build your story around that. Also, pay attention to the relationships between the characters. The friendship and budding romance between Ladybug and Cat Noir are important elements. Don't forget to add some twists and turns to keep the readers interested. Maybe a character they thought was a friend turns out to be working for the villain.
It could still be Hawkmoth. Since he's always after the Miraculouses, he might find a way to turn Cat Noir evil and use him as a tool to finally get Ladybug's Miraculous. So Hawkmoth would be pulling the strings in the background while Cat Noir does his dirty work.