Lau (劉, Ryū; Chinese Pinyin: Liú) is a Chinese nobleman, British branch manager of the Shanghai trading company "Kong-Rong," operator of opium dens, and top official of the Chinese syndicate Qīng Bāng.
In order for Lau to conduct business in England's "underworld," he must follow Ciel Phantomhive's orders to the letter. That being so, Ciel has left the administration of the oriental quarter, the East End, and black market docks to Lau.
As a Chinese nobleman, Lau dresses in sumptuous Chinese clothing, which includes a Changshan. He has a natural inclination to keep his hands hidden and clasped together in his "capacious" sleeves—hidden within them is a certain needle, which he describes as "an instrument of oriental medicine."
Lau is, generally, an easygoing and carefree man, who frequently smiles and indulges in smoking opium. He is, on numerous occasions, accompanied by several women. He refers to his personal assassin, Ran-Mao, as his sister, although they are not related by blood.
Lau has a peculiar tendency to say or act like he is aware and well-informed of something important, only to later reveal that he is, in truth, clueless. This particular trait of his often annoys others around him; Sebastian Michaelis believes that Lau just chimes in whenever "he thought it appropriate."
Lau has a strong propensity toward violence, which he showed when he told Ciel Phantomhive that he would kill Agni if he were Harold West Jeb, much to Ciel's surprise, since he, on the other hand, found that to be a bit excessive. While Ciel was willing to spare Harold and Mina, Lau was not as forgiving and had Ran-Mao terrorize the both of them. Also, in his zeal to help Sebastian with a magic trick, which involved sticking multiple swords in a chest that Sebastian was in, he did so without thinking of the consequences—he even immediately attacked from the top; Sebastian later admitted that Lau had actually managed to deal minor pain to him, a demon.
Black Butler Arc
Lau engages in a meeting with Ciel Phantomhive, Chlaus, Angelina Dalles, Azzurro Vanel, Arthur Randall, and Diedrich. They discuss the issue about a malicious "rat" and the necessity of it being eradicated, implying that a drug-dealer is among them.
Red Butler Arc
At Ciel's London townhouse, Lau, with Angelina Dalles and Grell Sutcliff, loot for tea leaves. Sebastian Michaelis accommodates them with tea, and they gather to discuss the recent string of murders so vicious that the killer was given the nickname "Jack the Ripper".
Lau points out that the murderer is definitely an "abnormal madman", and he questions if Ciel is daring enough to investigate the gruesome crime scene. He opts that they go right away, but when Angelina asks him for the location, he reveals that he, too, does not know where the crime scene is.
Consequently, Ciel suggests a certain place for information, and they arrive at the funeral parlor of Undertaker. When Undertaker appears out of his custom-made coffin, he frightens Lau, Angelina, and Grell. They are directed to sit atop the coffins, and Undertaker agrees to share information, but only for some form of compensation. Lau asks him how much money he wants, and Undertaker vigorously approaches him to declare that he does not care for the Queen's money. Undertaker tells them to amuse him with the finest of laughs; Lau attempts to do so with a Chinese-influenced joke, but he fails. Sebastian later steps up, requests for them to wait outside, and forbids them from peeking inside. Lau and the others perceive strange noises coming from the funeral parlor, and afterwards, with Sebastian's permission, they enter to see Undertaker laughing wildly. Undertaker, then, reveals to them that all of Jack the Ripper's victims have had their internal organs removed with medical precision (Lau is also skeptical of his drink as Undertaker might have stored a kidney in the container).
On the carriage ride home, Sebastian is ordered to compile a list of suspects, and departs, impressing both Lau and Angelina. Ciel asserts that Sebastian will definitely be able to accomplish his mission, and that he will have tea prepared for them as well. Lau comments that Ciel must be confident of Sebastian because since a long time ago, he has always been at the Earl's side, never leaving him- "like a shadow". Ciel then points out that Sebastian has not served him for even two years yet.
They return to Ciel's townhouse late because Grell traveled the wrong way. Lau and Angelina are dumbfounded to see that Sebastian has already returned home first, with the tea and preparations finished. They listen with admiration as Sebastian reads off the blacklist of suspects. They chat, while having tea, and Sebastian, paying close regard to the conditions, narrows down the possibilities to Aleistor Chamber.
That evening, they arrive at Aleistor's party. Angelina and Grell attend the party as themselves, Ciel as Angelina's niece from the countryside, Sebastian as Ciel's home tutor, and Lau as Angelina's lover. Afterward, Lau is obliged to fan Angelina as she indulges in luxury.
Sebastian, to serve as a distraction for Ciel, pretends to be a magician and asks the "random" gentleman, Lau, to assist him in the performance. Lau agrees, and Sebastian instructs that after he enters the cupboard, Lau is to tightly chain it up and then pierce the cupboard with several swords. Sebastian promises to come out alive, and after he goes inside the cupboard, Lau says he will not hold back. He immediately stabs from the top, bewildering the audience. He then swiftly applies the chains and thoroughly penetrates the cupboard with swords. Despite this, Sebastian steps out alive, and he and Lau receive the audience's passionate acclaim. Lau and Angelina praise Sebastian, and the former lightheartedly says that he had believed he killed Sebastian with his "mountain of needles". He curiously asks if there was some sort of trap, which causes Angelina to scold him for shoving all the swords at Sebastian without a thought. Nevertheless, Sebastian assures them both that he told them there were no tricks or traps.
The following day, they discover that Aleistor is not "Jack the Ripper." Lau muses that if the suspect could not have carried out the murders, then others from the beginning are responsible for them. Later, Lau comments that the stormy night is "pitiful".
Subsequently, Lau attends Angelina's funeral and visits Ciel by her grave. He questions if he has revealed who the murderer was to the Queen, but Ciel states there was no reason to since the Jack the Ripper killings have stopped. Lau declares that this decision will cause him to "steadily sink into the mud" because of his refusal to seek help. Ciel retaliates by saying Lau's opium and intoxicants den, in time, will surely be closed by the police. Lau asserts that he can find a new business venture, as his interest in England and in Ciel is "far from exhausted"; he adds that he hopes Ciel will show him many more interesting things. They then part ways.
Indian Butler Arc
Ciel and Sebastian, after learning about the Anglo-Indian attacks, go to visit Lau in his opium den to see if he knows of any Indian hideouts. There, Lau is relaxing with Ran-Mao and several girls. Ciel scolds him to stop smoking opium and listen, and leaves East End to Lau since the number of people who move in and out of the street are under his management. They walk to East End to find the stronghold of Indians, but Lau soon admits he has lost track of where they are at while listening to Ciel's explanation of the incident.
They are then attacked and threatened by Indians, and Lau conceals himself on top of a roof and watches the ensuing fight and the arrival of Soma Asman Kadar and Agni. After Agni defeats all the Indians and subsequently departs with Soma, Lau praises Sebastian and Ciel and claims that he was hiding on the roof for the "right chance to jump in". He comments that Soma and Agni are definitely not from the East End due to their elegant apparel and accent.
Afterward, Lau returns with Ciel to his London townhouse. There, they encounter Prince Soma and Agni again as the pair have decided to stay with Ciel since they "saved" him; Lau also decides to stay with Ciel. Soon, they learn that Agni and Soma are looking for Mina, and throughout the day, he joins Soma and Agni as they interrupt Ciel during his lessons at whatever available opportunity.
At fencing hour, Ciel challenges Soma to a match. During the match, Agni intervenes and unintentionally hurts Ciel's arm in the process. Lau tosses a sword to Sebastian and tells him that he should take reprisal for his master. However, after the match, Agni and Sebastian are tied, much to Lau's disappointment.
The next day, another mysterious attack occurs, and Lau points out that Soma and Agni have been suspicious from the start. They decide to wait until nighttime to investigate Soma and Agni who usually leave every night. Lau, Ciel, and Sebastian then follow them, and they discover that they are simply looking for Mina.
Later, however, Agni leaves on his own; Lau, Ciel, Sebastian, and Soma follow him as they are all unaware of his motive in going out arbitrarily at night. They eventually end up at Harold West Jeb's house, who is an importer of trade goods, and Lau notes that they are in the same business. They sneak onto his property with Sebastian lifting Ciel over the wall while Lau and Soma are forced to climb over. Lau soon calls them over to the entrance, as he has already knocked out the guard personnel by rendering them asleep with a needle soaked with a drug- an ancient Chinese technique. When they respond in a disapproving manner, he nonchalantly states that at least the guards are not dead.
They go inside, and eavesdrop on Harold and Agni. Later, when Soma bursts in, he watches the ensuing fight. Lau and Ciel deduce that Harold is involved in the black market, so Lau concludes that this matter is in Ciel's jurisdiction. Sebastian rescues Soma while wearing a stuffed deer's head, which amuses Lau. When Lau deems it too dangerous to remain there, he carries Ciel out and back to the townhouse. There, they speculate that Agni betrayed Soma in order to earn Harold the Royal Warrant, and in return, Harold would release Mina.
Ciel decides to obtain the Royal Warrant for the Funtom Corporation, and Lau agrees, saying that launching into food industry will also deter competitors. However, Soma announces that Agni's "Right Hand of God" will be unbeatable and claims he has never tasted a more delicious curry than Agni's; Lau and Ciel derive that his nickname is not conceived in respect to his strength, but rather because of his god-like capability in preparing curry.
Later, as directed by Ciel, Lau uses his position as the head of a trading company to obtain the best spices in a short period of time and complains that he had to prepare them all in one day despite not being an expert in spices. Ciel counters that only on occasions such as this is Lau beneficial, and Lau concedes that it is never a bad time to do Ciel a favor. He then also aids in taste-testing the curry until Sebastian can make a competition-worthy one.
Lau follows Ciel to the kitchen, where Ciel requests that Sebastian prepare him chocolate cake for a dessert. Out in the hall, Lau comments that the inconvenience Ciel has imposed on Sebastian seems to indicate that he would like Sebastian to lose. Ciel says it would be more interesting than obtaining the Royal Warrant if he did, and Lau calls him a bully.
At the competition, Lau arrives with Ran-Mao, and he introduces her as his sister although they are not related biologically. They speculate the possibility of the disclosure of Harold's dishonest deeds by Agni should he be released. Lau then asks if Ciel would kill Agni if he was Harold, and the latter finds it excessive. Lau casually states that if it was him, he would do as such, and he adds that he is intrigued by Sebastian's strategy in the curry contest.
After the competition is declared a tie between Agni and Sebastian, the Queen arrives to cast her own vote. When reminded of her dead husband, she breaks down crying; Lau comments that she seems like a complex character, and Ciel admonishes him. After she has recovered, she officially announces Sebastian as the winner. Seeing Harold's distress upon losing, Lau follows him and Mina to an alleyway. He remarks that while Ciel would let them go, he must discipline the "naughty little mice" that made a mess out of the East End. Hence, he keeps a "cat", referring to Ran-Mao, who violently swings her clubs. They scream, promising to never repeat the offense.
Phantomhive Manor Murders Arc
Lau and Ran-Mao are invited to a party thrown by Ciel Phantomhive. There, he introduces himself to Arthur Conan Doyle, and tells him that though Ciel is moody, something interesting is bound to happen. When Ciel introduces the other guests to Lau, Patrick Phelps is shocked to hear that Lau manages the Kong-Rong Company, but he goes silent when Lau glares at him. When Ran-Mao flirts with Georg von Siemens, Lau attributes her bold action to her supposedly pampered nature. He and the other guests are impressed by Grimsby Keane and Irene Diaz.
In the midst of the festivities, Grimsby and the other guests hear a loud scream from Georg. They rush to his bedroom; inside, they discover, to their unanimous horror, that Georg has been killed. After Baldroy and Finnian move Georg's body to the cellar, Lau points out that the storm will keep the Scotland Yard away and that they are probably trapped in the Phantomhive Manor with the murderer. They contemplate about the details of the murder, and Lau suggests that Georg's death is a locked room murder. When Karl Woodley and Grimsby start fighting, he easily stops them and asks everyone for their alibis. When it is his turn, he says that he and Ran-Mao were drinking in the lounge with Karl. Ciel does not have an alibi, and Lau relays his suspicions about Ciel. He then proposes that they confine Ciel for the time being, to ease everyone's anxiety. However, he refuses to be the one to watch over Ciel; to make sure he does not escape he nominates Arthur instead. Afterward, Lau and the other guests are escorted to their respective rooms.
The next morning, Lau and the other guests discover the brutal murder of Sebastian Michaelis. Lau notes that it must have been impossible for the confined Ciel to have committed the murder, and he adds that things "just got interesting"; Arthur, who is beside him, is shocked by Lau's sinister smile. Soon after, the guests examine Sebastian's body. When Lau comments about the savagery of the murder, Finnian emotionally demands that they stop, as they are discussing the appalling details in front of Ciel. They decide to move Sebastian's body to the cellar for the meanwhile and plan to pursue the topic at breakfast.
Later, at the breakfast table, they realize that Patrick is absent. They head to Ciel's bedroom, where Patrick was assigned to stay in. When they find that the door is locked, Grey swiftly cuts it down, to Lau's amazement. They hurry inside, and discover Patrick's corpse. While everyone else is concentrating on Patrick, Lau and Ran-Mao rummage through Ciel's wardrobe, much to Ciel's annoyance. Soon after, they have dessert in the drawing room where they discuss the three murders. Ciel voices his suspicions about Lau, which are derived from the facts that Patrick was Lau's business rival and that Lau carries around a large needle that could have inflicted the wound they saw on Patrick. When Lau displays his needle, Karl and Grimsby rashly jump to the conclusion that Lau is the murderer. Lau explains why he cannot be the murderer and wonders aloud if Ciel is taking revenge on him; Ciel assures him that he is simply teasing him for suggesting his confinement earlier. When Karl goes berserk at the idea that there is most likely more than one murderer, Tanaka effortlessly suppresses him with a move Lau recognizes as Japan's "baritsu."
Ultimately, the group allows for Arthur to dictate their actions from here on out, as through deductive reasoning, he is the only one who could not have committed any of the crimes. They decide to investigate Sebastian's body in the cellar, but Lau asks to stay behind to enjoy tea with Ran-Mao. Subsequently, Arthur explains to all the guests that their rooms and belongings must be checked, and they give their consent; Lau is the last room Ciel and Arthur inspect for the male side, and just like the other rooms, they do not find Sebastian's key. The group gathers in the drawing room once again, and Lau hypothesizes that the key could have been thrown outside; this prompts Finnian and Mey-Rin to volunteer to search outside. Afterward, Lau suggests the idea that there is a thirteenth person in the the manor, and that he is probably waiting for the right moment to strike.
Soon after, Jeremy Rathbone, the "thirteenth person," is brought to them, much to their astonishment. Lau claims that even he did not expect for the thirteenth person to show up so soon, but he then demonstrates that he does not have a clue to who the thirteenth person is. After they verify that Jeremy is not involved in the murders, Jeremy is allowed to lead the investigation.
For dinner, the group eats a scrumptious steak meat the Phantomhive servants have prepared. Lau presses for the truth behind the incidents, but Jeremy advises them to not be hasty.
While Jeremy implements a plan to catch Patrick's killer, Lau and the rest of the party members accumulate in Karl's room and wait. After a while, Patrick's killer is revealed to be an African snake that has been trained to attack whoever or whichever harbors Ciel's scent. Lau says that if Ciel had died, he and Ran-Mao would have been in trouble. They soon deduce that the snake must have been smuggled, which brings their attention to Karl, who specializes in the African diamond trade. Karl tries to put the blame on Lau, but Lau rebuts the accusation by stating that Kunlun does not do business with African companies. Jeremy has enough evidence to pin the murders of Georg and Sebastian on Karl. After Karl is detained, Lau joins in on the toast to celebrate the solving of the case. He and the other guests later safely leave Ciel's manor.
Luxury Liner Arc
One morning, Lau and Ran-Mao barge into the Phantomhive Manor, startling Ciel Phantomhive. Lau expresses his disappointment that Ciel has already finished his breakfast, for he was planning to eat it. He offhandedly notes that he thought Sebastian Michaelis had died recently, and Ciel scolds him for not listening.
After he is seated and given food, Lau reveals that he has come to discuss the Karnstein Hospital, which reportedly revives the dead, as claimed in the newspaper. He informs Ciel that the hospital has been doing a lot of shopping in the back docks he is in charge of. The hospital often illegally shops for foreign slaves, but the amount has increased abnormally as of late. He voices his doubt that a hospital could fit so many people, and he comments that it is disastrous for such an underhanded hospital to feature in the regular society's news. With this information, they speculate that the hospital is conducting illegal human experimentation, and Ciel orders Sebastian to investigate. Afterward, Lau and Ran-Mao take their leave.
Public School Arc
Lau and Ran-Mao go to Weston College to observe the annual cricket tournament. There, Ran-Mao holds up a betting board while Lau attempts to persuade other spectators of the tournament to place bets on whether Scarlet Fox or Sapphire Owl will win the match.
Later, Lau, with Ran-Mao sitting in his lap during Ciel's final match with Green Lion, is flanked by several other women. Upon seeing the women display their bare legs, the Green Lion players become flustered, which is actually all part of Sebastian and Ciel's plan of inducing poorer performance from the opposing team, so that they can easily win the match. After a certain informer reports them to the officials, Lau and his women are forcibly taken away from the venue. Despite this, they are later able to witness Ciel's victory and the birth of a second "Miracle of Sapphires."
- (To Ciel Phantomhive) "— And thus, do you become further mired in mud. Even if you reach a place from whence you cannot return, you will never utter an unsightly scream or beg for help in front of anybody. You proud hound of the Queen. I shall be careful myself to avoid falling into my lord's care.'"
- (To Ciel Phantomhive) "I am still interested in this country. And in you as well, my lord. I expect you will continue to amuse me."
- (To Harold West Jeb and Mina) "Lord Earl said to leave the small fry alone, but those who try something once will try it again and again. He's still too soft when it comes to that sort of thing, I guess. Well, I do find his boyish side rather lovable. But I must strike some fear into the hearts of the naughty little mice who made a mess of my garden here, in the East End. That's why I keep this cat. Meow!"
- "The spider's web has already been woven. The more you struggle, the harder it becomes to escape from those bonds. Whatever the prey, once they get involved with me, catching them is only a matter of time."
- "In this world, Earl, there're people who can't survive because of the cruelty of reality. I sell those people's dreams."
- "In this whole world, everything is the dream of a butterfly."
- "One night, Zhuang Zhou dreamt he was a butterfly. He was a happily fluttering butterfly. It was so much fun. He could fly wherever he wanted. And he had no thought of being Zhou, but suddenly he woke up, and was startled to find that he was now Zhou. He couldn’t decide: Was he Zhou who’d dreamt he was a butterfly or a butterfly now dreaming he was Zhou? Between being Zhou and a butterfly, surely there must be some distinction. This is what we call the transformation of things."
- According to the official Kuroshitsuji character popularity poll, Lau is the ninth most popular character in the series, with 268 votes.
- The only time Lau wore something different from his Chinese clothing was when he went to Aleistor Chamber's party as Angelina Dalles's lover, dressed in a traditional suit.
- Lau was included in the list of possible Jack the Ripper suspects Ciel Phantomhive made. It is unclear why that is because Lau is not known to have the medical expertise required to commit the crimes. However, Angelina Dalles did mention that orientals like Lau were under suspicion due to their skill in the use of needles and familiarity with human anatomy.
- According to Yana Toboso and her editor Mr. K, Lau is the character who underwent the biggest development during the early stages of the series, because, at first, he did not have much of a personality. However, this changed after Koji Yusa started voicing him. Without him, Lau would not be like he is now, and he would not have become an important character in the series.