Question: is kalluto zoldyck a girl?
Answer: Despite wearing a furisode, typically a traditional dress for Japanese women, Kalluto is a boy: The 2004 databook seems to say that he is a boy with the tidbit: 「将来性豊かな着物少年」 (lit. "A kimono-wearing boy with a lot of prospects.") Mizaistom refers to Kalluto as the fifth son of the Zoldyck Family.