Q-chan is a little bat-like creature and is D's constant companion. His name is perhaps derived from the sound he makes – "kyū". He is the only creature in the shop that looks like an animal to everyone (almost all of the other animals look like strange humans to Chris and the Count).
After being hinted at through the series, Q-chan's true identity is revealed in Volume 10 as Count D's Grandfather, and the proper holder of the title "Count" and name "D". He tells Eva Braun at the end of the first volume of the sequel series that the title of Count was received in his own grandfather's time, and is now simply the name of his store.
Although we never see the name in the English translation of the series, he is often referred to in fandom as "Sofu D," "sofu" meaning "grandfather" in Japanese. Upon the end of the series, "Q-chan" reverts back to his humanoid form (identical to D apart from his two golden eyes) and takes the reborn Count D's father to raise.