War for Cybertron, Cybertron, Several Million Years Ago

Optimus Prime swerved as a monstrous hand crashed into the cybernetic matter adorning the surface of Cybertron. He transformed and rolled as he was flipped upward from the limbs force. He glanced backward at the gigantic robot. 

It was huge. Not just huge, but gigantic. Muscular limbs aligned the monstrous body, shaped like a strange dinosaur, particular a tyrannosaurus, muscular, huge, powerful, and black. The creature was all black, with some purple rising through it, and a gigantic Decepticon insignia centered right on its chest. Then there was the head... 

A monstrous head, just as terrifying as the body. It clearly fit with the body. It was tyrannosaurid in stature and appearance. In its mouth was an extremely powerful cannon and laser, able to be fired as soon as it opened its horrid mouth. Atop it's head was a strange orange-yellow crest, running from the back of the snout, to the other end of the head.

Then there was a tail, an enormous tail. It boasted a spiked end with a large laser. The tail also was loaded with dark Energon crystals, capable of corrupting and binding any cybertronian, and turning them into its slaves, only wishing to do its bidding.

But despite its terrifying look, Optimus still faced it. He knew, however that he couldn't face it alone, earlier he had brought in Bumblebee and Ironhide, and they faced it together. 

"Prime!" A young voice screamed out to Optimus, and he instantly recognized it as Bumblebee's. "How do we kill this thing? Everything we've tried seemed to just make it tougher. If only we had a weapon to combat it! Maybe then we could turn the tide..."

In truth, Optimus did believe he had a weapon that could stop the creature. He also believed the only way to stop it was at his old weapon's expense. He needed to make a choice: sacrifice his powerful axe, with power to possibly destroy Dark Energon, or  sacrifice millions of innocent lives and save it to use it to end Dark Energon and the Decepticons forever.

He also knew when he made the choice to become an Autobot so many years ago he already made this choice.

I've made my choice.

Prime charged at the beast, ready to end it forever...

Somewhere in the Mid-Pacific, Oceania, March 23rd, 1977

In the dark, a single gasp broke a cavern's silence and echoed throughout as a single creature shot up off of the cavern's damp and cold floor. Suddenly, the speaker found herself on her knees, gasping and struggling for breath, as if she had just been revived from being unconscious.

She continued to struggle for breath until another creature, of a similar build came to her aid.

48th Presidential Inauguration, Washington DC, The United States of America, January 20th, 2029