One week had passed since Marceline and Kira made the deal with each other. She was now his Lady Boss while the vampire king just became a mere bodyguard.
Kira chose to keep his real identity hidden from Marceline for now. He didn't trust her fully yet to reveal that he was the king of all vampires. Fortunately, Marceline had forgotten about it when he accidentally mentioned it to her during their first encounter. She had no recollection of it, even their first kiss.
Besides, he was trying to keep her safe from his enemies. It would be best for her not to know the identity of the vampire king. He wanted his enemies to believe that he was already dead.
Rebel vampires were being hunted by Dominique's people. If they learned that the Vampire King was alive then they would start looking for him.
Once they found out Marceline's connection to him then her life would be in danger. The werewolves might target her just like what they did to her parents.