I got to know about this anime about two weeks ago.I've been busy so I could only watch the first few episodes.Although watching the first episode does not motivate you to continue watching the story, the story gets better and better.You guys should seriously watching trust me, it's awesome if you love supernatural anime(and it contains a bit of blood of course, as the name suggests).


Here's the story :-
Under the care of her adoptive family, Saya Otonashi has been living the life of an anemic amnesiac, but otherwise ordinary schoolgirl. However, her happy life is shattered when she is attacked by a Chiropteran, learning that she is the only one who can defeat them. Armed with her special katana, Saya embarks on a journey with her family, allies, and her chevalier Haji, to rid the world of the Chiropteran threat and recover her identity. The course of the journey reveals the background history of the Chiropterans and Saya's past, which extends into the mid-19th century.
The series is initially set in September 2005 Okinawa City (Koza), on Okinawa Island, near the US Kadena Air Base. Over the course of the series, Saya travels across the world, from Japan to Vietnam, Russia, France and finally the USA, fighting Chiropterans.


find more info on :-  
http://en.wikipedia.org/wiki/Blood+


I'm not giving any links though(since it's illegal) and its not in crunchyroll(find a place to watch it yourselves)