
Q, also known as Kyusaku Yumeno in Bungou Stray Dogs, is not given any defined gender, and most of the time, Q is pronounced as They/Them.
Bungou Stray Dogs follows Atsushi Nakajima, a young man with the power to transform into a tiger. He joins the Armed Detective Agency, a group with special abilities that solve mysteries and fight crime. They often clash with the Port Mafia, a dangerous criminal organization. The series is known for its unique characters and also has many other characters, like Q, whose gender is not defined.
Disclaimer: This article may contain spoilers for some. Readers are advised to continue at their own discretion.
Source: KADOKAWAanime
Who is Q in Bungou Stray Dogs?

Kyusaku Yumeno, who is also known as Q in the Bungou Stray Dogs series, is part of the Port Mafia, which is a criminal underground group.
Q gender is not specified, and they go by the They/Their/Them Pronounce. They joined the Port Mafia at the age of six and can control their minds. Due to their unpredictable nature, they were sealed away but released during a war with the Armed Detective Agency (ADA) and The Guild. Q targeted ADA members but was stopped by Dazai Osamu. Later, Q was captured by The Guild and used in a plan to destroy Yokohama. Dazai and Chuya Nakahara nullified Q’s ability, saving the city, and Q was detained again.
Q has two-toned hair, with white on the left side and black on the right. Their eyes have different-shaped pupils: a yellow star on the right and a yellow ring on the left. Q wears a small hat tilted to the left, a white shirt, a black coat, suspenders, beige shorts with red stripes, brown shoes, high white socks, and a red sling bag with a cat or dog design.
Q (Kyusaku Yumeno) Ability

Q's ability is called “Dragon Magra” which can control the mind of anyone they bump into, which first starts causing the person pain, and after that, the ability activates to make them feel hallucinated and like they see many things.
Q's ability has an additional stage where they carry a special doll. Anyone who harms Q will suffer from the Harm ability and potentially die.
One of Q’s fights against H.P. Lovecraft. In a surprising twist, Q attempted to use their mind-control ability on Lovecraft, only to find that he was immune. This unexpected turn of events led to Q’s capture by The Guild.
FAQs on gender of Q in Bungou Stray Dogs
A. There are 61 episodes released in the Bungou Stray Dogs.
A. In episode 19 Q (Kyusaku Yumeno) debuted in the Bungou Stray Dogs series.
A. No, the Bungou Stray Dogs anime series is not finished yet.