While the "Transformers" animated series came to an end in America in 1987 after "The Rebirth", production was continued in Japan with three new, exclusive animated series spin-offs to continue the story. The first of these series, "", supplanted the events of "The Rebirth". With the Decepticons defeated, the Autobots entered into an even closer relationship with Earth. The Autobots also began the colonization of other worlds, the first of which was the planet Athenia, where Optimus Prime was stationed. It soon became apparent, however, that the consequences of releasing the energy of the Matrix to cure the Hate Plague were more far-reaching than Optimus had anticipated. Without the energy of the Matrix to act as a balancing factor, Vector Sigma had become destabilized. The Decepticons suddenly returned to exploit this, assaulting Cybertron in order to seize control of the mega-computer. Prime took a squad of troops to aid in the battle on the planet. When the arrival of the Autobot Headmasters tipped the battle in their favor, Prime broke off from the main attack and headed down into the depths of the planet, planning on stabilizing Vector Sigma at any cost.