Well, perhaps in the fanfiction, the reunion is not as smooth as expected. There could be some tension among the characters due to past differences. Sonia might be angry at Sonic for leaving them years ago, and Manic could be caught in the middle. They then have to work through these issues while also facing a new threat that has emerged in their absence.
Well, a plot might involve Sonic from Sonic X getting lost in the world of Sonic Underground. He has to adapt to the different rules and characters there while also trying to find his way back home. Along the way, he forms new friendships and discovers new abilities within himself. It could be a story of self - discovery and cross - universe adventure.
Sonic, Sonia, and Manic are usually the main focus. They are the core of Sonic Underground and in the reunited fanfiction, their relationships and how they come back together are often explored.
There might be a fanfiction where Sonic, Sonia, and Manic team up with some unexpected allies from other Sonic series. For example, they could join forces with Tails and Knuckles to face a super - powerful villain that none of them could defeat alone. This would bring a fresh dynamic to the Sonic Underground universe.
One possible plot could be that the characters from Sonic Underground get transported to the world of Sonic X. They then team up with Sonic and his friends in Sonic X to fight a common enemy like Dr. Eggman who has somehow become even more powerful by combining technologies from both universes. The different Sonic characters would have to learn to work together, sharing their unique abilities and skills.
One interesting Sonic X Underground fanfiction could be about an alternate universe where the characters have different powers. For example, Sonic might have the ability to control time briefly in addition to his speed. Another could focus on the relationships between the characters, like a deeper exploration of the bond between Sonic and his siblings in the Underground setting. And there might be a fanfiction that combines elements from different Sonic series, creating a whole new adventure for Sonic X Underground characters.
One interesting story could be about Tails using his mechanical skills to upgrade the Sonic Underground's vehicles. He might create some high - tech gadgets that help them in their adventures against Dr. Robotnik.
One interesting crossover could be a race between Naruto and Sonic. Naruto could use his Shadow Clone Jutsu to try and outwit Sonic's speed. Another could be a team - up against a common enemy. For example, if a powerful villain from the Naruto universe like Orochimaru teamed up with Dr. Robotnik from Sonic Underground. They would have to combine their skills, like Naruto's ninjutsu and Sonic's spin - dash, to defeat them.
Sonic himself would be very interesting. Since there are two different versions of Sonic in Sonic Underground and Sonic X, it would be cool to see how they interact. They could have a friendly competition about who is faster or better at saving the day. It would also be interesting to see how Sonic from Sonic X reacts to Sonic Underground's family dynamic, as Sonic in Sonic X is more used to his friendship with Tails and Knuckles.
A common theme is adventure. Both Sonic X and Sonic Underground are about Sonic and his friends going on exciting adventures, and this is often carried over into the fanfiction. For example, they might be on a quest to find a powerful chaos emerald or save a new world from an evil villain.
One idea could be that Sonic Underground's siblings get separated in a new zone and Shadow accidentally stumbles upon them. He initially thinks they are enemies but then realizes they are on the same side against a common foe. Another could be that Shadow is on a mission related to the Chaos Emeralds and crosses paths with Sonic Underground. They end up having to team up to stop a new villain who wants to use the power of music and the Chaos Emeralds for evil.