He would destroy the universe to keep her safe. She would become death to protect him.
Terran medic Rachel Pryne was designed by the Ohnenrai to destroy their pursuing foe before all life in the known galaxy and beyond falls prey to its aggression. Ohnenrai leader Ehtishem Mahle was tasked with deploying Rachel into their deadly enemy's path. Falling in love with her wasn't part of the plan, but now he desperately needs a way to wield this weapon without ending her life.

The only possible solution to galactic extinction lies with Rachel and Ehtishem, but all they want is to survive and be together. Everyone else can go straight to hell.