Saya Otonashi is a seemingly normal high school girl who discovers a dark past of an ageless chiropteran born in 1833. As part of the Red Shield, she fights to stop the evil designs of her twin sister, Diva.
Saya appears in the movie Blood: The Last Vampire and the resulting anime Blood+ , however the portrayal of the character in each could not be more different. In The Last Vampire we learn very little about Saya as for the majority of the movie she is cold an emotionless and is purely driven by her desire to find and kill the Chiropterans. She has a tendency to become distressed when she comes into contact with religious paraphernalia and gets angry toward anyone who mentions God in her presence, this is one of the few times she shows any emotion. She fights with a katana sword and displays superhuman strength and speed and also heightened senses, this coupled with the fact that David refers to her as "The last remaining Original" would suggest she is not human, and in the final scene of the movie we see a picture of her dated 1892.
In Blood+ however we meet a very different character. Saya at first seems to be a happy, normal high school girl, who enjoys life and cares for the people around her. This dramatic change in the character is explained as the movie is set a few months before the start of the Vietnam War and Blood is set in present day and Saya has no memory of her life before a few years ago. During the first few episodes Saya learns that she is not like everybody else and that she is the only person alive who can kill the Chiropteran monsters. Horrified and scared by this revelation Saya is initially reluctant to fight and is afraid that uncovering the secrets of her past will bring her more pain and misery. Both Hagi and David know the truth about her but they both decide it is best for Saya to uncover the truth herself. As the series progresses she learns more about herself and accepts her mission to destroy the Chiropteran and towards the very end of the series she is more like she was in The Last Vampire, cold and non-talkative, choosing only to focus on her mission.
She is a skilled athlete and fighter and her katana is specially made with an edge she can touch that draws blood from her hand and distributes it across the length of the blade. We eventually learn that it is Saya's blood that gives her the power to kill the Chiropterans.