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 that the reader is a new inhabitant in Sonic's world and has a special power that Sonic needs to help save the world. They embark on a journey to find a way to control and use this power effectively, facing various enemies and challenges along the way. Their relationship grows as Sonic teaches the reader about his world and they learn to trust each other.
One idea could be a Sonic fanfic where Sonic and his friends travel to a parallel universe where the roles are reversed. For example, Eggman is the hero and Sonic is the villain. It would be really cool to see how they handle this new situation.
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.
One idea could be that Sakura Akatsuki discovers a magical lemon tree in a hidden garden. The lemons from this tree have special powers that can heal any wound. She then has to protect the tree from those who would use its power for evil. Another could be that Sakura Akatsuki is on a journey and she meets a strange character who is always surrounded by lemons. This character gives her a lemon that transports her to a different dimension where she has to face various challenges to get back home.
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 idea could be that Sonic accidentally enters Equestria where Rainbow Dash lives. They could then have a race to see who is faster in the new and unfamiliar terrain for Sonic. Rainbow Dash might be amazed by Sonic's speed and Sonic could be intrigued by Rainbow Dash's ability to fly while racing.