Well, obviously Sonic and Eggman are the main characters. Sonic is the speedy blue hero, always ready to save the day. Eggman, on the other hand, is the brilliant but often - misguided inventor. In fanfiction, their relationship can be re - imagined in many ways.
One interesting plot could be Sonic and Eggman having to team up against a new, more powerful enemy that threatens their world. They put aside their differences and combine their unique skills, like Sonic's speed and Eggman's inventions, to defeat the foe.
Tails would be the first one to come to Sonic's aid. His intelligence and flying ability would be very useful in finding Sonic and getting past Eggman's defenses.
A common theme is the battle between good and evil, with Sonic representing good and Eggman representing evil. They constantly fight over things like power, territory, or the Chaos Emeralds.
A really cool Sonic and Eggman fanfiction could be set in an alternate universe. In this universe, Sonic is not the hero he is in the main canon. Instead, he's more of an anti - hero, and Eggman is the one trying to save the world from Sonic's reckless behavior. It flips the traditional roles and makes for a very engaging read.
In this kind of fanfiction, Sonic might be locked in one of Eggman's elaborate traps. Eggman could be planning to use Sonic's speed for his own evil experiments or to finally defeat him once and for all. Sonic would surely try to escape using his wits and speed.
Fanfiction.net is also a great place. There are many Sonic the Hedgehog related fanfictions there. You might need to do a bit more digging to find the really good ones about Sonic and Eggman, but it's definitely worth exploring as there are thousands of stories available.
Sure. One popular Sonic X Eggman fanfiction is 'The Battle for Chaos Emeralds'. It has an interesting plot where Sonic and Eggman are in a constant struggle for the powerful Chaos Emeralds. Another one is 'Eggman's New Scheme' which shows Eggman devising a very elaborate and unexpected plan against Sonic and his friends.
Sonic would be the first to react. He'd be angry and immediately start the search for Tails. Amy would be worried sick and might try to help Sonic in any way she can, like gathering information from the other animals in the area. Knuckles would be on high alert, thinking this could be part of a bigger plan to get to the chaos emeralds. He'd guard the emeralds even more closely while also keeping an eye out for any signs of Eggman's activities related to Tails' kidnapping.
There could also be some new characters introduced in this fanfiction. Maybe a mysterious figure who has some inside knowledge about Eggman's operations. This new character could either help Sonic or cause some trouble depending on their motives. Another possibility is a group of creatures native to the area where the battle takes place. They could be initially scared of Sonic and his friends but then end up helping them in some way.