Nightwalker: The Midnight Detective 1998

Shido's a midnight detective, half human and half vampire with no real memory of his past, who specializes in solving supernatural murders.Joined by Yayoi Matsunaga, a female government agent, Riho Yamazaki, an orphaned teenage girl working as his secretary and Guni, a little green imp, Shido must face demonic creatures known as Nightbreed.