A story could revolve around Sonic and Elise finding a magical object. This object has the power to change the balance in Sonic's world. They have to decide what to do with it. Elise, with her gentle nature, might want to use it for peaceful purposes, while Sonic is more concerned about the potential misuse by his enemies. They have to work together to figure out the best solution, which could lead to a lot of character development and exploration of their relationship.
A unique take on their relationship can make it stand out. For example, if the fanfic focuses on how Elise's calmness affects Sonic's impulsive nature in a new and interesting way. It could show how they learn from each other and grow as characters.
Another plot could involve Antoine having to team up with an unlikely character. For example, he teams up with a villain who has a change of heart temporarily. Together they face a greater threat that endangers the whole Sonic universe. This would create an interesting dynamic between them as they learn to trust each other.
One idea could be that Amy initially sees Metal Sonic as a threat but then realizes he has some sort of glitched 'conscience' and tries to help him. For example, she might notice that he is being controlled against his will in a way and tries to free him from that control.
One idea could be Sonic crossing over with another popular game like Mario. Sonic could find himself in the Mushroom Kingdom and have to team up with Mario to stop a new threat that combines the chaos emeralds and power - ups from both worlds. Maybe Bowser has teamed up with Dr. Eggman to create this chaos.
Another idea is a story where Cream discovers a new power within herself while on an adventure with Sonic, Vanilla, and Lemon. This new power could be related to some ancient energy source in their world. And the story could revolve around her learning to control it with the help of her friends and how it changes their dynamic.
Maybe there's a device that combines the chaos emeralds' power with Chemical X. This causes a strange rift in the dimensions, bringing Sonic and the Powerpuff Girls together. They have to work together to reverse the effects of this strange combination. Sonic uses his speed to gather the scattered chaos emeralds, and the Powerpuff Girls use their powers to keep the villains from interfering.
One idea could be that Sonic accidentally enters the world of Equestria Girls while chasing Dr. Eggman through a strange portal. He then teams up with the girls to stop Eggman from stealing the magic that powers their world. Another could be a race between Sonic and Rainbow Dash which gets interrupted by a common enemy.
One idea could be that Katniss, Peeta and Lemon find themselves in a situation where they have to work together to survive in a new, uncharted territory. Maybe there's a new type of danger that the Capitol has created and they have to use their combined skills to overcome it.
One plot idea could be Botan discovers a magical lemon grove that holds the key to a hidden power. She has to overcome various challenges to protect this grove from an evil force that wants to use the lemons' power for bad. Another could be a comical story where Botan tries to make the most delicious lemonade using her unique skills, and along the way, she meets some wacky characters who either help or hinder her.
Perhaps a story where a lonely baker during Christmas discovers a crate of lemons. He decides to use them to make a new type of Christmas treat. As he bakes, he meets a mysterious stranger who helps him create the perfect lemon - infused Christmas cookies. Through this process, the baker finds new friends and a new sense of purpose during the holiday season.