Nightwalker: Midnight Detective (Night Walker -真夜中の探偵-)

Mankind is threatened by a race of creatures called the Nightbreed, people who have succumbed to supernatural beings. Hunting them down is a vampire named Shido. With the help of an urban spirit and his naive secretary, Shido stands as a vanguard against the Nightbreed, while also trying to untangle his own murky past.