One interesting Miraculous Ladybug fanfiction in the US could be one that explores different relationships between the characters outside of the main storyline. For example, a fanfic might focus on how Marinette and Alya's friendship develops in new and unexpected ways. Maybe it shows them going on adventures together that are not related to the usual akuma battles.
One possible fanfiction could be: On Heroes Day in Paris, Ladybug and Chat Noir were on high alert. The city was bustling with excitement and anticipation. Ladybug noticed that Hawk Moth seemed to be planning something big. She quickly swung through the city, looking for any signs of trouble. Meanwhile, Chat Noir was charming the citizens, making them feel safe. As the day went on, a strange akuma appeared. It was a giant, menacing creature that started to wreak havoc. Ladybug and Chat Noir joined forces, using their special powers and teamwork to defeat the akuma. In the end, they were celebrated as the true heroes of Heroes Day.
In fanfiction, the Miraculous Ladybug characters could interact with the UN in multiple ways. First, they could be invited to give a presentation on the nature of akumas and how they've been combating them. Then, they might be part of a task force created by the UN to deal with a global akuma - like threat. Ladybug would use her leadership skills, while Chat Noir would bring his charm and combat skills. They would also interact with UN staff, learning about international laws and regulations regarding superhero activities. And perhaps they would even help in training other heroes from around the world who are brought together by the UN.
You can start by looking on popular fanfiction websites like Archive of Our Own (AO3) or FanFiction.net. Just use the search bar and type in 'Miraculous Ladybug' along with any specific tags like 'US - based' or the names of characters you're interested in.
One possible plot could be that Ladybug and Chat Noir are invited to the United Nations as representatives of Paris. They give a speech about the importance of unity in the face of akuma attacks. Meanwhile, Hawk Moth tries to send an akuma to the UN building but Ladybug and Chat Noir, with the help of new international superhero friends they make at the UN, manage to stop it.
Perhaps on Heroes Day, Hawk Moth decides to use the positive energy of the day against Ladybug and Chat Noir. He creates an akuma that can absorb the love and admiration that the people have for the heroes. As the akuma grows stronger, Ladybug and Chat Noir find it difficult to fight. They have to find a way to turn the people's love back into a strength rather than a weakness for the akuma. Meanwhile, they also learn more about their own powers and how they can be enhanced during this special day. They start to involve the citizens more in their fight, making Heroes Day truly a day of heroes working together to defeat evil.
Maybe a new character from another country comes to Paris. This character has a Miraculous that has powers related to nature. Their role would be to bring a new element to the team. They could use their powers to heal the damaged parts of Paris that were affected by Hawkmoth's attacks, and also help in battles by using nature - based defenses like thick vines to trap villains.
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.