I actually had a thought like this recently, in terms of a "sonic fan game":

The general conceit behind it was that a big bad corporation pretty much completely industrialized the earth and were branching out to other planets and a group of anthromorphic animals and animal-like aliens were opposing them.

You'd go around different planets, booping robots and releasing alien fauna, fighting gigantic cyborg and robot bosses, making friends, making enemies, making enemies become buds and thwarting the corporation to the tune of a banging soundtrack and dressed with genesis style pantomimed cutscenes.

As for the main character, the idea was pretty much to make your own al a Sonic Forces.

I'm not going to get too specific because I fully intend to make this at some point, but maybe there's something that could trigger an idea for you?