If you don't really care about the background of this fanfiction, you can skip this and go straight to the story in the next chapter. If you wish to stay, then let me tell you all about my AU.
In my AU (I don't really know what to call it specifically) Robotnik/Eggman is the "king" of Mobius. As the king, Robotnik brainwashed all of the citizens, so he can be in total control. This includes replacing memories, necessary worship, and force. Of course, not everyone will fall for his tricks (Sonic and the gang). Those who rebel against him are to be roboticized or killed.
Before he had became king, he had fought with the Mobians and defeated them, specifically Queen Aleena (the mother of Sonic, Sonia, and Manic and the original ruler of Mobius). Aleena had to separate with her children due to the danger that Robotnik had put them in, which kinda follows the storyline of Sonic Underground. The triplets still haven't found their mother so they cannot overthrow King Robotnik just yet… yet.
Unlike in all the Sonic series/games, Sonic, his siblings, and all freedom must hide their identity (with masks, special abilities, or Manic's/Tails' special equipment to change appearances). If their identity were to be revealed, the brainwashed citizens would do everything in their power to capture them to please Robotnik. The Resistance is a group of Mobians who are trying to reveal the truth about Robotnik's ways and stop his sick and twisted rules.
Knowing of the Resistance's existence, Robotnik created a program that is a mixture of government and police work, which is called Analytical Mobian Society Division (or AMSD). Their task is to find and capture members of the Resistance.
There are no other worlds/dimensions, like where Blaze and Chris Thorndyke come from. There are no other humans besides Robotnik. Blaze the Cat and Marine the Racoon are from a different country, where Blaze is the ruling princess, and they are also helping Sonic and his crew regain their true royal leaders and freedom. Silver is still from the future and he only comes to inform Sonic if their future actions are correct or not. Other characters live in Mobius and are spread across the country.
Now about how everyone is dressed. They can literally wear whatever they want, but they can't be "naked". For example, Sonic only wears his shoes and his pair of gloves (and maybe some other added accessories) in other games/shows, in my AU he would be considered to be "naked". Now throw a jacket or a shirt on him and he's "clothed". Weird, right? I know. Male species aren't exactly required to wear pants because nothing inappropriate is seen (unless they are aroused), females, on the other hand, must wear bottoms and tops. Sonic in my AU still doesn't wear pants because of his unnatural super speed. Whenever he runs, his pants will most likely be set on fire because of the friction. Uniforms are different. Everyone, no matter the gender, must wear the bottoms and the tops.
Another thing in my AU is the fact that there are special abilities that are not meant to be used in Robotnik's eyes because they could easily overthrow him from his throne. Not everyone obtains a special ability because of the lack of use (Well, they don't know that they have the ability). An example of a special ability: Sonic's has the rare ability of Super Speed, or in their Latin name (as they must be referred to by an AMSD Agent), Super Celitras. Rouge's special ability is Jeweled Eyes (Insignem Gemmis Oculis Meis), the ability to easily find jewels (It's like an x-ray in her eyes, but she can only find jewels, which is very helpful when trying to find chaos emeralds. There are various different special abilities and I will delve deeper into it throughout the story.
Speaking of chaos emeralds; Of course, after all the seven chaos emeralds are used, they are scattered about to unknown locations. In my AU, instead of scattering all over the world, they only scatter within Mobius. The same is with the Sol Emeralds, which will only scatter about in her country, so there is no confusion. If someone finds a chaos emerald and comes into contact with it, their body won't be able to withstand the chaotic energy, so the emerald will consume their body and the emerald will dangerously increase their ability. There are only a handful of people who can physically touch the emeralds without being affected by their chaotic power (Sonic, Shadow, Knuckles, Blaze, Robotnik, etc.). If someone isn't immune to the emeralds' power, then they must obtain a special set of gloves to be able to hold the emerald (Tails, Rouge, Amy, Sonia, etc.).
If you finally reached the end of my AU explanation and you have questions, don't be afraid to ask. I don't mind clarifying anything that may confuse you all.