Well, it could be about Ladybug and Chat Noir finally revealing their identities to each other and having to deal with the consequences. Maybe they face a new, more powerful villain that is a threat to all of Paris and they have to use their combined powers in new ways.
One possible plot could be that Hawkmoth has finally been defeated, but a new evil force rises from the ashes of his downfall. This new enemy has studied Hawkmoth's methods and is even more devious. Ladybug and Chat Noir have to not only fight this new threat but also repair the damage that Hawkmoth caused to Paris over the years, both physically and emotionally.
Perhaps in the future fanfiction, Ladybug and Chat Noir have retired and a new generation of Miraculous holders emerge. These new heroes have to learn from the stories of Ladybug and Chat Noir while facing modern threats like digital - based villains or threats from outer space. They might struggle to live up to the legacy of the original heroes.
In a 'Watching the Future' Miraculous Ladybug fanfiction, Ladybug and Chat Noir might see their future selves facing a super - powerful villain. They could then start training harder in the present to be better prepared.
It could involve exciting new Miraculous powers for Ladybug and Chat Noir. Maybe in this 'Peak Future' they have mastered their existing powers to an extreme level, like being able to combine their Lucky Charm and Cataclysm in a more powerful and unique way.
A new villain could be a former Miraculous holder who turned evil due to some misfortune. Maybe they felt betrayed by the Order of the Miraculous and now seek revenge. Another possibility is an alien entity that is attracted to the power of the Miraculouses and wants to use them to conquer Earth.
One plot idea could be that Ladybug and Chat Noir see a future where Paris is in ruins because they failed to stop Hawk Moth. This would give them the motivation to find a new strategy in the present, like seeking out new allies or uncovering a hidden power of their Miraculouses.
One idea could be that Hawk Moth finally manages to get hold of both the Ladybug and Cat Miraculouses and the heroes have to find a new way to fight him, perhaps by teaming up with some of the minor characters who develop new powers. Another could be that Ladybug and Cat Noir have to travel to the future to stop an even greater threat that is related to Hawk Moth's actions in their present time.
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.
One possible plot could be that Jagged Stone discovers the true identities of Ladybug and Cat Noir. Maybe he gets involved in one of their battles accidentally and then becomes determined to help them keep their secret identities safe while also using his fame to distract Hawkmoth.
The fanfiction could center around a new student who is secretly a villain in disguise. They try to disrupt the school play which is about the Miraculous Ladybug and Chat Noir's adventures. Ladybug and Chat Noir have to figure out who the new student really is and stop their evil plan before the play is ruined.
One possible plot could be that Ladybug and Cat Noir, in their civilian forms Marinette and Adrien, have a sleepover with their friends Alya and Nino. During the sleepover, they play some Miraculous - themed games. Maybe they create their own Miraculous - inspired challenges, like a kwami - hiding game where they have to find a small object representing a kwami. And then, late at night, there could be a false akuma alert that turns out to be just a malfunctioning Ladybug - themed alarm. This could lead to some comical moments as they all scramble to 'transform' before realizing it's a false alarm.