Killian is the last hybrid of his kind.

He is a vampire/human hybrid. Scientists forced him from his home and chained him up.

Blindfolded him to not see.

Gave him injections and modifications that ensures that his hybrid genes remain strong while making him very verile.

You, on the other hand, are a beautiful young woman.

You don't have to much money, conditions were bad enough for you to attempt robbery.

Though you were caught.

Instead of sending you to prison they found in your medical records you're off the charts fertile.

They threw you into the dungeon with Killian, forcing you to breed him and continue the hybrid species, not allowing you to remove the chains and not caring to much for your health.