Accel

Accel ends up in the Floating Castle after being ambushed by a gang in a town of outlaws — who tied him to a hot-air balloon and let him loose in the skies. After regaining consciousness, he finds himself inside the castle with a Power Stone in his hand. Upon realising its power, the masked gunman vows to escape and take his revenge — on both the one who imprisoned him and the thugs who sent him there in the first place.