Ladybug would likely be the most important. She is the main hero and has the power of creation. In the final battle, her ability to think on her feet and come up with creative solutions using her Lucky Charm will be crucial. She also has the leadership skills to rally the other Miraculous holders.
In the 'the final battle miraculous ladybug fanfiction', perhaps there is a twist where Hawkmoth teams up with an unexpected villain from the past. This forces the Miraculous heroes to not only fight a stronger enemy but also deal with the complex dynamic of two villains working together. Ladybug has to come up with a new strategy that involves all the different Miraculous powers at their disposal.
I think Chloe could be really interesting. Since she was Miracle Queen, exploring her motives and her internal struggle would add depth to the story. Maybe she wasn't fully in control when she became Miracle Queen and there's more to her actions than meets the eye.
Chloe could be really interesting. Since she has been the Bee Miraculous holder in the show, exploring her growth and redemption through fanfiction would be great. We could write about how she uses the powers of the Bee not just for herself but for the greater good of Paris, and how she overcomes her insecurities and bratty behavior.
An akumatized villain could be the main character in a different kind of fanfiction. The villain was once a normal person but due to some heartbreak or injustice, they are akumatized into a dragon - like form. The story could then be about their journey of redemption or how Ladybug and Chat Noir try to bring them back to their normal self.
Maybe one of Ladybug's classmates who is also a cheerleader. For example, Alya could be a cheerleader in this fanfiction. She already has a nose for news and is friends with Ladybug, so she could use her cheerleading skills to get closer to the action and help Ladybug in a different way.
A new ice - themed superhero could be introduced. Maybe someone who has the power to control warm air to counter Glaciator's ice powers. This character could be a young scientist who was working on a climate - control project when they discover their powers. Another option could be a villain who is jealous of Glaciator's power and wants to steal it for themselves. They could have a fire - based power which creates an interesting contrast with Glaciator's ice.
Obviously, Ladybug could be the main character. Since it's about cleaning the house, she could be shown in a more domestic side of her life, which is not often explored in the original series.
Ladybug could be the main character. Since she is the main protagonist in the original series, it would make sense for her to be in the center of this fanfiction. She could be the one to witness the car accident, or be directly involved in it somehow, like trying to stop it from happening with her powers.
A new character who is a skilled acrobat could be a great thief. They could use their acrobatic skills to easily get in and out of places unnoticed. Their backstory could be that they grew up in the circus and had to turn to thievery due to some misfortune.
Obviously, Harry Potter is one of the most important. His role as the Chosen One is central to the final battle. Hermione Granger also plays a crucial part with her intelligence and knowledge of magic. Ron Weasley too, as he provides support to Harry.