Well, in a Miraculous Ladybug Civil War fanfiction, it could start with a misunderstanding about a new villain's origin. Ladybug and Chat Noir might have different views on how to handle it. Ladybug could be more cautious, thinking it's a trap, while Chat Noir is eager to prove himself and wants to jump right in. Their different stances could cause other holders of the Miraculous to take sides, creating a civil war - like situation.
One possible plot could be a rift within the Miraculous team. Maybe there's a disagreement over how to use the Miraculous powers. Some might think they should be more aggressive in fighting villains, while others prefer a more diplomatic approach. This could lead to two factions forming, just like in a civil war.
It could be a Miraculous holder who has been corrupted by the power. They might start to think that they should be the sole leader and use the civil war as a means to take over. For example, if a holder of a powerful Miraculous like the Bee Miraculous turns bad, they could be a formidable antagonist.
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 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.
Maybe Ladybug and Chat Noir have finally defeated all the major villains and they are now retired. They could be passing on their Miraculous to a new generation of heroes. Paris has become a much safer place with the lessons they've taught about good and evil.
One possible plot could be that Marinette, in an overzealous attempt to get closer to Adrien, creates a 'trap' of sorts. Maybe she arranges for a photoshoot at a location where only she and Adrien are present, under the guise of it being a school project related to fashion. She could have set up the set in a way that Adrien would be impressed by her creativity and they would have an extended period of time to talk and bond.
The plot could be that Ladybug and Chat Noir are transported to an alternate Paris where dancing is the key to saving the city. They must perform a perfect Ladynoir dance to break an evil spell. Along the way, they face challenges like learning new dance moves and dealing with their own insecurities.
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.
One possible plot could be that an evil villain discovers a new power that can turn Ladybug into stone. Ladybug is caught off - guard during a battle and gets turned. Chat Noir then has to find a way to reverse the spell. He might search for a magical artifact or seek help from other Miraculous holders.
Perhaps the large cockroach is actually a guardian of an ancient Miraculous that has been lost for ages. Ladybug and Chat Noir encounter it while on a mission, and at first they're freaked out. But as they learn more about it, they realize it's trying to protect the Miraculous from falling into the wrong hands, like Hawkmoth's. So they have to work with the cockroach to keep the Miraculous safe.