MoMo -the blood taker-

In Tokyo, suspicious cases are occurring where the victims have all of their blood drained from them.
Mikogami Keiji, a detective who also wants revenge for his lover, killed 10 years ago, pursues the culprit, the “Man with two faces”.
What is the identity of the silver-haired girl who observes him…?

Assistant: Hoshikawa Danpa