A car thief could be the main character. After stealing a high - tech car, something goes wrong during the getaway and he turns into the car. Now he's stuck in this form, and the people he stole the car from are still after him. He has to use his new abilities as a car to evade capture while also trying to figure out how to reverse the transformation.
Well, the plot could start with a young mechanic who is always around cars. One day, while working on a very special vintage car, there's a strange energy surge. The next thing he knows, he is the car. He experiences life from a different perspective. He can't speak in the traditional sense but tries to convey messages through his headlights and horn. He discovers he has new senses, like being able to detect mechanical problems in other cars just by being near them. He goes on a journey to find a way to turn back into a human while having many encounters with different people and cars along the way.
It could be another monster who is jealous of Sans' new form. This monster might feel that Sans is getting special treatment or opportunities because he's now a human. So, this jealous monster tries to find a way to either turn Sans back into a skeleton against his will or make his human life miserable by causing trouble for him in the human world, like spreading false rumors about him.
Dr. Eggman would be an obvious choice. Since Sonic is now in a more vulnerable human form, Eggman could see this as the perfect opportunity to finally defeat Sonic and take over the world. He might come up with new devious plans, like creating robots specifically designed to target a human Sonic.
Perhaps there could be a jealous teacher in the school where he starts working as a human. This teacher is threatened by Koro Sensei's popularity among students, even though he's now human. So, this teacher starts to spread rumors or create problems for him to get him fired.
It could be another monster who is jealous of Sans getting all this new - found attention as he turns into a human. This monster might try to stop the transformation process or make Sans' life difficult in his new human form.
Maybe a kind-hearted storyteller. They have the ability to communicate with the animals in the Lion King world through their stories. The animals are fascinated by the human's tales and the storyteller uses this to bring peace and unity among different animal groups, especially during times of conflict. They could also use their stories to inspire Simba to be a better leader.
A regular person, say a factory worker in a dystopian society where there is no hope. One day, she discovers a secret resistance group that is trying to change things. She decides to join them, and through her own growth and the group's influence, she transforms from a despairing individual to a beacon of hope for others. This shows how an ordinary person can be the main character in such a story.
Dipper Pines could be one of the main characters. He might be the one who first discovers Bill's transformation and tries to figure out if it's a trick or if Bill is truly changing. His inquisitive nature would make him a great foil to Bill's new human self.
It could be a simple village girl. She might be kind, with a love for nature, which catches Legolas' attention. Maybe she has a special talent like being able to communicate with animals, which is something Legolas admires.
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.