Before joining Red Shield, David was the sole survivor of a chiropteran attack on his special forces squad. His father was also a member of Red Shield and was one of Saya's victims in the Vietnam incident. It is implied that he, along with Joel, are the only members that are descended from a line of Red Shield operatives. He is aware of Saya's past life and wishes to use her in the struggle against the chiroptera. David's red crystal item is a cross.   David tends to be straight-faced and serious, with a cold personality. However, he also assumes an unofficial guardianship of Kai and Riku, and would be instrumental in helping Kai come to terms with what Saya is and with Riku's conversion to a chevalier. He seems to take a particular interest in helping Kai grow up to be a strong man who can support Saya and Riku as their brother, despite their unusual natures.    ~!When the Red Shield's headquarters are destroyed and Saya is believed to have gone down with it, David sinks into a deep depression and becomes an alcoholic. Kai helps him get back on his feet, though, and he returns to his duties slightly more cheerful and able to smile than he had been before.   During the investigations into one of Cinq Flèches's lab, he finds Julia and she tells him something about the research they are doing. He talks to her briefly again at Amshel's party, and lets her know that she will always be welcome back with the group.   Towards the end of the series, Dr. Collins tries to murder Julia, but David protects her, getting critically wounded himself. Julia keeps vigil over him in the hospital, and after he recovers they begin a romantic relationship.   At the end of the series, Julia is pregnant with his child. !~ (Source: Wikipedia) 

Saya Otonashi, a seemingly normal high school student, suffers from amnesia and she can't remember the past year of her life. One day, after a man appears and gives her a katana sword, her destiny begins to be revealed. 
 
Soon she finds herself fighting the latest threat to humanity - Chiropteran monsters, ravenous immortal creatures that can change their form, disguising themselves as human beings. They feed off blood and hide themselves within the human world. An organization known as the Red Shield has been waging a private war to wipe them out and now the struggle has grown. Saya's journey for the truth has begun. 
 
(Source: Sony Pictures Home Entertainment)

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A Brazilian voice actor. Known for voicing Might Guy in Naruto, Scar in Fullmetal Alchemist, Hyouga in Shurato, and Alucard in Hellsing

Teropterids are evil beasts which pose as humans and live only to drink human blood. Fortunately for the human world there are groups dedicated to destroying them. A brooding and mysterious girl named Saya is the best teropterid slayer there is, and now, in 1960's Japan, she is sent to a U. S. army base which may be infested... 
(Source: Anime News Network)

Saya, the main character, lost her memory and has been living with her adopted family. Her everyday life seems quite normal, except that she eats a lot more than she actually needs. Then one day she meets a guy named Hagi in a park. She is told that he has been searching for her, for a long time. Since then, her normal life has changed completely. (This manga series is proceeding quite a bit differently from the anime) 
A high school girl named Saya can not remember anything from her past. A handsome young man, Hagi, appears and something seems familiar about him. This girl is more than human with an ancient and mysterious past. She will hunt down and kill the monsters called Chiropterans.

It is the official novel adaptation of the anime series. It expands on the events of the anime and gives greater background information on the battle against chiropterans.