Blood+: One Night Kiss is based on the Blood+ (pronounced as "Blood Plus"), an anime series produced by Production I.G. and Aniplex and directed by Junichi Fujisaku. This game and its sequel is currently only available in Japan and has not been licensed for release in any other countries.
The game features cel-shaded graphics in the same style as Killer7 and is set in the fictional town of Shikishi. Players spend most of the game playing as Saya, occasionally switching to Aoyama, an original character created for the game.
Source: Wikipedia, "Blood : One Night Kiss", available under the CC-BY-SA License.