Rustblaster

Rustblaster (ラストブラスター) is a manga series by Yana Toboso. It was serialized in GFantasy from October 2005 to March 2006, and is complete in one volume. Yen Press has licensed it for English release.

Plot
In the Vampire Mercenary Specialized School, "1000 Years Academy," the most unvampire-like vampire at the academy, Aru, and the human transfer student, Kei, meet by chance. But what they didn't know was that it was a fate the world depended on.