Chiropterans are hematophagous bat-like creatures that live by feeding on human blood. These grotesque vampires are the primary focus of the Blood franchise, specifically Blood: The Last Vampire and the Blood+ anime/manga series.
In Blood: The Last Vampire, the origins of chiropterans are never explored. In Blood+ however, chiropterans are created when human beings are injected with the blood of Diva, the last pure-blood chiropteran. Diva's blood is usually contained within products manufactured by the pharmaceutical company Cinq Flèches and causes a slow, gradual transformation from human to chiropteran. The process can be sped up using enhancements like Diva's voice. Chiropteran bodily fluids are infectious, so people wounded by chiropterans may also undergo a partial metamorphosis.
Chiropterans generally possess extraordinary speed, strength, and supernatural healing abilities. They are also capable of contorting and transforming various body parts, in order to fly, or have longer limbs. Higher level chiropterans have the ability to disguise themselves as ordinary humans.
Chiropterans can heal almost instantly from most wounds. Thus, bullets are non-lethal and are only capable of slowing them down. Explosives as well prove to be ineffective and/or non-lethal. However, if buried or sealed inside stone they will go into hibernation until freed.
Ironically, the blood of a chiropteran queen is also the primary method of killing them. When the blood of another queen is introduced into a chiropteran's bloodstream, it starts a crystallizing chain reaction that destroys them. Thus, chiropterans created from Diva's blood can be killed by Saya's blood, and vice versa. Another way to eliminate a chiropteran is by decapitation, even though it is believed not to be a viable method for humans but it does give a much higher chance of success than the use of bullets. Chiropterans are severely weakened when they lose blood, so inflicting major damage in a minimal amount of time will ensure they suffer dramatic blood loss and die quickly.