Chanto Suenai Kyuuketsuki-chan

ちゃんと吸えない吸血鬼ちゃん

As a vampire, Luna Ishikawa can be considered a unique transfer student. With her cool demeanor, she has quickly become her class' center of attention. Normally, it would be nearly impossible for Tatsuta Ootori—a completely average guy—to ever interact with her. However, this changes when the two are unexpectedly paired together for cleaning duty!

After Tatsuta spontaneously forms a friendship with Luna, his impression of her slowly crumbles: she is not the mysterious and collected girl everyone thinks she is. In fact, she is unable to even suck blood properly! Resolved to help Luna overcome her ineptness, Tatsuta proposes to become her practice partner. Pumping life into their mundane school days, the duo gradually works toward their delectable goal, improving Luna's blood-sucking skills with every bite she takes.

(Source: MAL Rewrite)