Kojima Mitsu is in middle school, but she's so small that she looks like she's in elementary school! One day while she is is changing into a maid uniform for a school event (with not much success... the uniform is too big for her), she find a little bat blocked by the window and helps it. Suddenly an awesome guy appears in front of her! He is a vampire and as thanks for saving his "toy," he helps turn her into an adult (with a kiss).

(Source: Shoujo Manga Maniac)