In the city of New Meridian, home of the mystical Skull Heart. It is said that every 7 years the Skull Heart will grant one girl's wish, but if that girl is not pure of heart, she will find herself instead transformed into a powerful monster known as the Skullgirl. Even a selfless wish can be twisted in the most vile of ways.

And after a starship has crashed in New Meridian, Optimus Prime, being the only survivor, must stop the Skullgirl.