The battle continues in BLOOD+ VOLUME FOUR, more adventures as Saya Otonashi battles the evil Chiropterans!  A normal high school student who suffers from amnesia, her destiny is partially revealed when a stranger presents her with a katana. Soon she finds herself fighting Chiropterans - ravenous creatures that can change their form, disguising themselves as human beings. An organization called the Red Shield has been waging a private war to wipe them out. They travel to Ekaterinburg during the continued struggle, but no one's safe.