What I'd Do for You

After their return from the Allspark, Optimus's concern that he would cause a greater divide between the Autobots and Decepticons in the new planet resulted in him leaving Cybertron. Megatron, finding no greater purpose than bullying his weakened nemesis, goes with him, leaving the planet in the hands of the new governments led by Bumblebee and Starscream. They've been gone for a long time, their whereabouts entirely unknown.

Meanwhile, their old home has gathered more and more returning cybertronians. The political atmosphere has shifted. Soundwave is back from the shadowzone per Megatron's last request. The slavers Optimus and Megatron encountered have only grown more powerful.

A new and dangerous Autobot returns from the depths of space, initiating a disaster that forces Optimus and Megatron to return after years of no means of communication with their homeworld.

Primus bestows the matrix of leadership to a new Prime.