Mayonaka no Tantei Night Walker

Night Walker is a series that was created by Ayana Itsuki. It was initially created to be an erotic PC game by TomBoy and was later developed into an anime.

Most people are familiar with the 12 episode anime which follows the story of Tatsuhiko Shido, a vampire living in Yokohama (Japan). He is the owner of a detective agency and uses this position to protect humans from Nightbreed (demons) who try to possess them.  Shido was turned into a vampire by Cain. At first he enjoyed his new existence but eventually came to realize that Cain's indiscriminant killing was wrong and so left him. He has traveled the world, mostly alone, before settling in Japan in his current life. Cain, however, follows him and, despite Shido's attempts to be rid of him, will not give up on trying to bring Shido back to him, through violence or persuasion or whatever method he thinks might bring Shido back to him.

Shido is joined in his current life by Yayoi Matsunaga, an N.O.S. agent. Yayoi was scarred in a fire when she was very young. Her twin sister became possessed by a Breed. Shido happened upon them a few years later. Yayoi's sister eventually died but wished that Yayoi would get her perfect face. This wish was granted. In the present series Yayoi is aware of what Shido is and often feeds him.

Shido is also joined by Riho Yamazaki, who initially does not know what Shido is but eventually discovers his secret. She unwittingly becomes bait when Cain tracks Shido down and uses her to try to get him to return to his vampire ways. Shido turns Riho into a vampire after Cain mortally wounds her. In the final episode of the series Cain torments Shido with visions of a reality in which Riho has turned evil.

Finally Shido is often partnered with a small fairy like being called Guni. Guni joined up with Shido shortly before he came across a young Yayoi and she often helps him in exchange for being allowed to hide (live?) in his hair.

The anime series focused mainly on Shido's relationships with Yayoi and Riho as well as his troubled past with Cain. There was also a healthy helping of angst as Shido struggles against the darkness that comes with being a vampire. Each episode also focused on a "monster of day" and a one episode plot that Shido, as a midnight detective, would have to solve. These episodes often focused on emotional conflicts, such as a human trying to obtain something they desire be it fame or friend and thus allowing a Breed to possess them or feed off of them in exhange for getting that which they desired. Though never stated these plots mirrored Shido's own personal journey as he struggled against the desire to give in to his vampire nature (as he did in the past) versus trying to live a good (if lonely) life.

 Prior to the anime Nightwalker was produced as an erotic PC game by the same name. In this first incarnation Shido is a quarter vampire who has been fated to protect the passageway between the mortal realm and the demon realm. He works as a private investigator and through this discovers that a girl was murdered by demons at St. Michael Academy. He goes there to try to find the demons and meets the girl's roommate, Riho. Yayoi is also in the game as a detective who had previously dated Shido. Guni is also present as Shido's familiar.