Lau is a tall Chinese man with short black hair and dark brown eyes that he almost never opens, a characteristic that adds to his enigmatic presence. He has a blue dragon tattoo on his left arm and habitually wears sumptuous traditional Chinese clothing, typically a Changshan, with his hands kept clasped and hidden inside his capacious sleeves. Inside one sleeve he conceals a needle, which he describes as an instrument of oriental medicine and which he uses with expert precision, leveraging his extensive knowledge of human anatomy to subdue people efficiently.

Professionally, Lau is the British branch manager of the Shanghai trading company Kong-Rong and a high-ranking executive of the Shanghai mafia syndicate known as the Qingbang. Under the authority of Ciel Phantomhive, the Queen's Watchdog, he serves as an Aristocrat of Evil, overseeing the Oriental quarter of London's East End, including the operation of opium dens and other illicit trade. His role in the story is that of a recurring ally and informant to Ciel, though his true loyalty lies with the Qingbang and his own interests, making him a figure of cautious cooperation rather than outright trust.

Lau's personality is marked by an almost perpetual, highly amused smile and a calm, laid-back demeanor. He speaks softly and acts relaxed in any situation, often making sarcastic or facetious remarks and presenting himself as though he knows more than he actually does. This deliberate ambiguity allows him to manipulate conversations and situations to his advantage. Despite his cheerful exterior, he is pragmatic, opportunistic, and mercenary: he does not perform favors without expecting repayment with interest, and he has a clear inclination toward violence when it serves his aims. He is unfazed by danger and enjoys dropping in unannounced at the Phantomhive mansion to observe or to make Ciel's life more interesting.

Lau's closest relationship is with Ran-Mao, a young woman he calls his little sister, though they are not related by blood. She acts as his personal assassin and constant companion, fiercely loyal and silently executing his orders. They are deeply comfortable with one another, and she accompanies him everywhere. His interactions with Ciel Phantomhive are characterized by a mixture of deference and playful mischief; he respects Ciel's authority but often tests his patience, and he refers to Ciel as Earl and to Sebastian as Butler. With Sebastian, Lau shares a mutual awareness of each other's dangerous capabilities, and their exchanges can carry an undercurrent of veiled competition.

In terms of development, Lau remains a consistent character throughout the series: a cheerful enigma whose backstory is largely unexplained, whose motivations are self-serving, and whose power and knowledge are greater than he outwardly displays. His notable abilities include his mastery of acupuncture and pressure points, which he demonstrates by incapacitating guards without leaving visible wounds, and his keen situational awareness, which allows him to notice details others miss despite his perpetually closed eyes. He is also a skilled businessman and strategist, adept at navigating both London's high society and its criminal underworld.