Nightwalker: The Midnight Detective

is an anime TV series created by Ayana Itsuki that is adapted from a PC game titled Mayonaka no Tantei Night Walker (真夜中の探偵 Night Walker).

Plot
Shido Tatsuhiko is not only a private eye... he is also a vampire with no real memory of his past. Joined by Yayoi Matsunaga, a female government agent, Riho Yamazaki, an orphaned teenage girl working as his girl Friday and Guni, a little green imp, Shido must face demonic creatures known as Nightbreed. Meanwhile, Cain, the vampire who made him what he is now, is seeking him...