One possible plot could be that Ladybug and Chat Noir are transported to the world of Frozen. There, they meet Elsa and Anna. Maybe they team up to fight a new villain that is causing chaos in both the Miraculous and Frozen universes. For example, a villain might be using the power of the Miraculous to freeze parts of Paris and also trying to take over Arendelle.
Another plot could involve Anna getting a Miraculous. She could be a new hero in Paris, teaming up with Ladybug and Chat Noir. They might face a villain who has the ability to create eternal winter like in Frozen, and Anna's experience with dealing with Elsa's winter could come in handy. Also, the cultural differences between Arendelle and Paris could add some interesting twists to the story.
Obviously, Ladybug and Chat Noir are the heroes in the Miraculous world, so they would be main characters. In Frozen, Elsa and Anna are the key figures. However, we might also see other characters like Tikki and Plagg from Miraculous having some interactions with the Frozen characters. For example, Tikki might be fascinated by Elsa's ice powers and try to understand how they work compared to the Miraculous powers.
One possible plot could be that Ladybug and Chat Noir are somehow transported to the Dark Souls universe. They find themselves in a desolate and dangerous land, facing powerful enemies they've never encountered before. Ladybug's Lucky Charm ability might work in strange ways, like creating items that have a different use in the Dark Souls world. Chat Noir could use his cat - like agility to navigate the treacherous terrains. Together, they have to find a way back home while also uncovering the secrets of this new and menacing realm.
Anna, being outgoing and adventurous, would probably get along great with Chat Noir. They could have a lot of fun banter and adventures together. When it comes to Elsa and Hawk Moth, Elsa's coldness (in personality as well as power) would be a contrast to Hawk Moth's manipulative and power - hungry nature. She would be very resistant to his attempts to use her for his evil plans.
A common theme is the contrast between the magical elements. In Frozen, it's the ice magic, and in Miraculous Ladybug, it's the Miraculous powers. Another theme could be friendship. For example, how the characters from both universes form new friendships.
In a Miraculous Ladybug and Marvel crossover fanfiction, the characters could cross - over in different ways. The heroes of Paris could be transported to the Marvel universe. There, they would have to adapt to a new world full of different super - heroes and villains. Ladybug might learn new fighting techniques from Black Widow, while Chat Noir could have a friendly rivalry with Spider - Man. Meanwhile, the Marvel heroes could also visit Paris and be amazed by the magic of the Miraculous.
It could be really exciting. Imagine Ladybug and Chat Noir teaming up with the Voltron paladins. Maybe Ladybug's Lucky Charm could help in a crucial moment during a Voltron battle, like finding a way to repair a damaged part of the giant robot. And Chat Noir could use his cat - like agility to outmaneuver the enemies that Voltron is facing.
A crossover could involve the kwamis getting interested in Batman's gadgets. Tikki might be intrigued by the Batmobile or Batman's utility belt. Meanwhile, Batman could initially be suspicious of these strange heroes from Paris. But as they work together, he realizes their power and the importance of their Miraculous. For example, Ladybug's power of creation could help fix some of the destruction in Gotham in a unique way.
One possible plot for a Miraculous Ladybug beach fanfiction is that Hawkmoth sends an akuma to the beach during a big surfing competition. Chat Noir is there to compete, and Ladybug has to show up and they end up having to fight the akuma while also trying to protect the civilians at the beach. They could also have some cute beach - themed banter in between the fight scenes.
One possible plot could be that the peacock miraculous has a new holder. This new holder might be a bit of an anti - hero at first. They could use the peacock's powers to create sentimonsters for their own gain, like stealing valuable items. But as the story progresses, they start to see the harm they're causing and slowly turn towards the side of good, joining Ladybug and Chat Noir in their fight against Hawk Moth.