Arne no Jikenbo

Arne Neuntöte is a vampire detective who manipulates supernatural powers. Lynn Reinweiß is a nobleman’s daughter who loves vampires. Their worlds should never have crossed, but they join hands to solve a bloody mystery.
In the darkest of nights, Lynn finds herself in desperate need of help. Then she wanders into the mysterious city of "Lügenberg", where non-humans live. Lynn's world changes drastically when she encounters "Arne", a vampire who is called "the worst" in the city. And tonight, a new "murder case" has occurred. What is the truth behind the bizarre incidents that take place in a world where humanity and the bizarre intersect?
"Come on, human. You may dance merrily under the crimson moon.”
(Source: The Case Book of Arne Steam page)