Chibi Vampire, Volume 1

Karin Maaka is a vampire with an unusual condition: instead of taking blood from humans, she must give them her blood instead! If Karin doesn't "donate" her blood often, she'll experience seriously intense nosebleeds. Her secret stays buried until Kenta Usui transfers to her class. Now her body produces more blood than ever before, and it looks like a reaction to him! Even worse, he soon discovers her true nature...