Luna is an assassin hired by yui's father to kill the sakamaki and mukami brothers and bring back yui. Luna and her partner duke arrive at the mansion and successfully get yui but as their about to escape they're stopped by all ten vampire boys. Luna tells duke to get away with yui and finish their job while she stays to kill the vampires. Luna is captured and questioned for where yui is but refuses to tell. Luna suffers from her past but she also smiles at it.
That's the one thing that luna heard as she became a prisoner of blood to the ten vampire boys.