Count Carlos is a half-demon, a hybrid of demon and human?! Sera, who was kicked out of the mansion where she had worked for 10 years overnight for discovering the Count's secret. Barely managing to find a new job, she ends up at the 'Xenogeneic Protection Management Bureau'. Sera, who became the caretaker of the vampire 'Vlad family', thought she would live happily with the xenogeneic beings, but… The previous caretaker stole the Vlad family's heirloom 'Red Gem' and ran away? Sera is threatened by the family to find the 'Red Gem'. By night a caretaker, by day searching for the heirloom, even a suspicious crown prince approaches Sera, who is struggling… Will the new caretaker Sera be able to safely retrieve the Red Gem?