A "fan theory / if Speed Battle had a story" of mine is either the Phantom Ruby was shattered into many pieces, or the game consist of collecting left over Phantom Ruby prototypes. That's why the goal of eacn stage is what appears to be a Phantom Ruby Shard.
When the Phantom Ruby shattered, it caused two things to happen:
- The dimensions to shatter, causing characters from other universes to appear. Such as a version of Sonic and Amy from a universe where they're baseball stars, or Sonic and Longclaw from the movie to show up.
- Spontaneous creations of replicas of everyone. Including Sonic, his friends and the visiting versions of themselves from the shattered multiverse. Because of this it's difficult to identify who is a replica or who is from another dimension.
So the game consist of you racing replicas/alternate versions of others as you must collect Phantom Ruby shards to restore the dimensions and proove who is the real deal.