Q-Chan is an adorable rabbit-like creature. Q-Chan is very friendly and likes D a lot, but doesn't really do much in the manga except be super cute and friendly. Q-Chan is not well liked by the officer, but is liked by some of the customers to D's shop. In volume four of the manga, it appears that Q-chan takes a human-like form as a girl, however upon closer inspection that character actually appears to be just a bat taking the form of a vampire, and not Q-chan, even though the character does look like Q-chan.

Spoiler

In volume ten of the manga, Q-chan reveals he is Count D's grandfather (and thus, male).