When Cinder was a young pug, she trained in her grandfather's dojo. She was at the top of the classes, alongside her rival and friend, Destro Magmastorm. When they were 14, she overheard Destro claiming that he had thrown their recent fight, claiming he couldn't hurt a girl. This enraged her so much, it set her on her life's path. She broke down the wall and hurt Destro in her anger, going so far as to break his back, making him unable to walk again. Then she left the dojo, never to return.
Destro had lost a lot that day... his legs, his crush... he spent years travelling the world in a desperate search for someone to give him his lower half again, and finally he stumbled upon the Deboss army. They healed his back, and bound him to their secret weapon, Ferocious Knight D, the Deathryuger. Their fates now intertwined, Destro's body is now the conduit to a monster, hellbent on finding Cinder. D wants to destroy her because she's Kyoryu Red. Destro wants to find her... and apologize.