The game is set in the continent of Babel, where the Tower of Babel looms large over seven nations. After the invention of alchemy led to its use as a tool of war that brought humanity to the brink of extinction, the seven nations struck an uneasy peace that led to a prohibition on alchemy for hundreds of years since. In the Continental Year 911, the nation of Lustrice broke the pact by assembling an army bolstered by alchemy, with ambitions of conquest over the continent. Led by Envylia, the six nations allied and struck down the rogue nation, casting alchemy once again to darkness. But 20 years after the war, alchemy once again begins to cause chaos in the land. 

(Source: ANN)

Aoi was raised as a normal boy on Earth. Little did he know he was the heir apparent to Mito, the Queen-turned-Space-Pirate of an alien race that chooses their sex at puberty! Aoi fell in love with Mutsuki, the police officer who was chasing Mito, and the three of them saved the Universe. The only side effect was that Aoi blossomed into a beautiful young woman.

Now a malevolent entity calling herself the true Queen of the Universe appears with enough power to destroy entire planets. Aoi must defend her new throne, but she needs Mutsuki's help. Mutsuki must come to terms with her own feelings for Aoi so they can defend Earth together and become the galaxy's first royal pair of queens.