Chocolate Vampire: Kuroyurike no Himitsu

The human girl Chiyo and the vampire Setsu have made a blood pact as children, which binds them together. Having grown up in the meantime, the two attend a school where vampires and humans are taught together. Recently, rumors about a dangerous drug called "Spice" have been circulating there. This drug is supposed to improve the powers of the bloodsuckers so that everyone is crazy about it. As a member of the campus security force, Chiyo is in charge of the investigation. But suddenly, unknown persons kidnap Setsu's brother! Does the culprit have anything to do with the drug...?

(Source: TOKYOPOP Germany, translated)