Sonic gets captured by Captain Gantu & Dark Oak, but escapes back to Earth and meets a young girl named Lilo and Experiment 626 aka Stitch (Sonic the Hedgehog belongs to SEGA, Lilo and Stitch belongs to Disney).
Offscreen Eggman kidnapped a young hedgehog and exprimented on him for a project to destroy his nemesis Sonic the Hedgehog. But the project never finished and the subject in question died and was left in a locked room when his base went under attack by Sonic and his allies and was abandoned
But then mysteriously the dead test subject soul was alive without a body and goes into the prototype badnik he was working on
Not knowing who he was he went tnto the world to find out who he is
His name is Shard and this is the story to find out who he is