One idea could be that Sonic accidentally gets transported to the world of Wonder Girl. He teams up with her to stop a common enemy that is threatening both their worlds. Maybe an evil scientist who wants to steal Sonic's speed and Wonder Girl's powers.
Perhaps there's a magical chaos that blurs the boundaries between their universes. Sonic runs into Wonder Girl while exploring the strange new world. She is initially suspicious of him but as they face various challenges like strange creatures and magical traps together, they form a friendship. Sonic uses his speed to help Wonder Girl reach places quickly and she uses her strength and wisdom to guide them through the unfamiliar territory.
One idea could be that Sonic accidentally runs into the world where Wonder Girl exists. He's confused at first but then realizes he can use his speed to help her in a battle against some powerful villains. Maybe he could use his speed to create distractions while Wonder Girl delivers her powerful blows.
A possible plot could be that a powerful villain creates a device that sucks Sonic from his world into Wonder Girl's. Sonic is disoriented at first but quickly realizes he needs to find a way back. Wonder Girl discovers him and at first mistakes him for a threat. But when they both notice the strange things happening around them, like the sudden appearance of dark energy blasts, they figure out it's the work of the same villain. They then join forces, with Sonic using his speed to scout and Wonder Girl using her combat abilities to fight. Eventually, they manage to defeat the villain and Sonic finds his way back home, but not before they promise to be friends and help each other if such a situation arises again.
Perhaps Sonic as a girl could have a story where she is trying to prove herself in a male - dominated racing circuit. She has to overcome doubts from others and show that she is just as fast and skilled as any of the male competitors. Along the way, she makes new friends who support her journey.
One idea could be that Sonic, through some magical or scientific accident, is transformed into a baby girl. In the fanfiction, his friends might initially be very confused. For example, Tails could be trying to figure out how to reverse the process while also taking care of Sonic in his new form. Sonic, as a baby girl, could have different abilities or limitations. Maybe she can't run as fast as before but discovers new powers related to cuteness or charm that help the gang in unexpected ways.
A possible fanfiction could focus on Wonder Girl's relationship with other members of Young Justice. For example, she might have a friendly rivalry with Superboy that turns into a strong bond as they face challenges together. This could include them training together and learning from each other's strengths and weaknesses.
The male OC could be a scientist who discovers a new form of energy that is somehow connected to Wonder Woman's powers. As they work together to understand this energy, they develop feelings for each other. Maybe the OC is initially a bit clumsy and not used to the world of superheroes, but Wonder Woman sees his potential and they bond over their shared curiosity.
In some fanfictions, they might explore the differences in their personalities. For example, Classic Sonic's more simplistic and straightforward approach contrasted with Modern Sonic's more complex and sometimes cocky attitude. They could start off not getting along due to these differences but then learn to work together. Maybe there's a story where they are both trapped in a strange dimension and have to rely on each other's skills. Classic Sonic's spin - dash and ability to handle more 2D - like terrains, while Modern Sonic can use his homing attack and boost in the more complex 3D areas of the dimension.
One idea could be that Sonic from Sonic X accidentally travels to the Sonic Boom universe and has to adapt to the different environment and new versions of his friends. Maybe he teams up with Sonic Boom Sonic to defeat a common enemy that has found a way to cross between the two universes.
One idea could be a race between Naruto and Sonic through different dimensions. Naruto could use his shadow clones to create distractions while Sonic zooms past. Another idea is a team - up to fight a common enemy that has the ability to disrupt both their worlds, like a villain who can steal chakra and chaos emeralds. Maybe Sonic could teach Naruto some of his super - speed techniques in exchange for learning some ninja skills.
One idea could be a crossover adventure where Sonic and Samus team up to stop a powerful, universe - threatening villain. They could combine their unique abilities, like Sonic's speed and Samus' combat skills and advanced weaponry.