Nothingness
Mobius.
A beautiful planet filled will all kinds of landscapes and life.
Left completely decimated by the Metal Virus.
Sonic had tried to save it. He really did. But his efforts were in vain. The world as he knew it was no more. All that was left was empty husks of what used to be living beings, turned to metal slaves called Zombots. All that Sonic could do now was watch as everything he knew and loved crumbled.
Sonic ran, and ran, until he could not run. He found himself in an empty field, with nothing but metallic grass as far as the eye could see. He collapsed, his body not being able to support his own weight anymore. His muscles ached, his head throbbed, and all he could do was to weep to himself. The guilt stung like no other pain he'd ever felt before. It was his fault all of this was happening. He knew that. Yet it stabbed him in the heart he knew he would never have again.
The virus was slowly spreading, making his skin burn like hellfire. His vision, blurred by the tears streaming down his face. The virus began spreading through his insides. Sonic could feel as his organs became nothing more than a metallic fluid. He felt like he was drowning in his own lungs. His world, slowly fading away. Yet it was nothing compared to the guilt.
"... I've failed... I'm sorry..."
Those were his final thoughts, would be his final words, if he could still speak, before his body went completely cold. Before his consciousness slipped away from him.
Before everything turned to nothingness.