Leon is a pure-blooded vampire that has chosen to peacefully coexist with humans. As a sign of his pure-blooded status, Leon shares a bond with a "deterrent," Noah. Noah's power suppresses the base instinct to drink human blood. Despite granting Leon this freedom, Noah still worries about his own unstable power and perceived weakness. Together, they investigate strange incidents and perform occult jobs. After all, even vampires have bills to pay.