Hirotsu is a middle-aged man with grey, swept-back hair, a mustache, and a short beard ending in a spike. His eyes are violet, with a monocle over his right eye, secured by a gold chain.
He dons a long, black coat over a white dress shirt with a black bow - his pants and shoes being the same color. Over the coat, he wears a dirt-brown scarf that's nearly the same length as his coat.
A chain smoker, Hirotsu always has cigarettes in his pocket.
A veteran mafioso, Hirotsu maintains a stoic, calm demeanor, often speaking with a certain degree of respect and formality towards even his opponents and targets. However, Hirotsu's brutality, beguiled by his composure, hasn't waned despite his age.
Befitting of the Port Mafia's higher ranks, Hirotsu's a ruthless and dangerous individual, and won't hesitate to kill in order to further their gains. Furthermore, he isn't above mocking others before killing them, sometimes with a smile. His experience in the Port Mafia leaves him particularly seasoned in its expectations of him and others, and as such expect diligence and promptness out of his subordinates. Otherwise, he has no qualms threatening their lives to keep them in line, especially when it comes to Gin Akutagawa and Michizō Tachihara's quarrels.
Hirotsu's nonchalance towards the Port Mafia's violent ways goes as far as his smoking habits, as he claims a cigarette always tastes best after "a job well done".
That said, Hirotsu takes his role and duty to the Port Mafia seriously. He values loyalty and ambition, specifically in Higuchi's case, when she insisted to save Ryunosuke Akutagawa from a rival organization. Although initially ridiculing her impulsive behavior, he respected her initiative and sense of duty, thus partaking in the rescue mission alongside Gin and Tachihara. Despite these facts, he seems to not harbor strong grudges against those who have defected from the Mafia, such as when he was seen willingly doing a favor for Dazai during the events of the Guild incident and speaking to him about it afterward.
His dedication to the Mafia has also been hinted to be towards the organization itself rather than its leader(s), evidenced from when he confronted Ōgai Mori about the conspiracy behind the former Boss' death and confided in him that the predecessor's murder was for the best lest Yokohama is turned into a blood bath and dragging down the Port Mafia down with it, despite the latter's defensive response. He also uttered "My soul is forever with the Port Mafia" before his supposed demise during his confrontation with a Hunting Dog.
Despite his strict nature, Hirotsu is notoriously protective of and caring towards his subordinates with Dazai noting that he is well known for "not getting rid of his subordinates easily" and being well-liked by several in the Mafia for this fact. He's protective and caring nature is shown particularly strongly towards his battalion leaders such as when he blasted Tanizaki for attempting to cut Gin and when he expressed relief that Tachihara had escaped from his confrontation with the Hunting Dogs safely.
- (落椿, Ochi Tsubaki?), cause things that he touches to fly backward with immense force. His ability, Falling Camellia
It has been shown that his ability is powerful enough to stop and bend steel pipes with just a touch. When used on a human body, besides launching it, it can even cause the bones to break.
Not much is known about Hirotsu's background, however, he has noted that he has been serving the Port Mafia from since before the previous Boss. He was 42 at the time of the death of the previous Boss and Mori's ascension.
Inside a warehouse, Hirotsu awaits the arrival of his subordinates. When they arrive, Hirotsu uses his ability on a metal door, the force sending the door flying. This startles a group of cargo men carrying unknown, heavy loads., whom Hirotsu politely greet, apologizing for "interrupting their work". The cargo men demand to know who he is, to which Hirotsu explains that the Port Mafia's heard rumors of their stolen goods being sold to the black market, said to take place in the warehouse, and is now "searching for evidence". When he attempts to do so, one of the men attacks with a steel pipe.
Hirotsu stops the attack with ease, the force of his ability sends the man flying backward. Hirotsu takes aggression as evidence. He approaches the man, who is shocked that the pipe is bent, asking if it's the first time he's seen an ability. Hirotsu promptly kills him, his body twisting and breaking right before the group's eyes. Lighting a cigarette, Hirotsu orders his subordinates to kill them all. Amidst the carnage of gunfire and death, Hirotsu nonchalantly comments on how there's nothing like a cigarette after a "job well done". The Mafiosi then explode any remaining evidence in the warehouse.
Soon afterward, Hirotsu arrives at a rendezvous with Michizō Tachihara, scolding him for being two minutes late, and soon after Gin Akutagawa. The two battalion leaders instantly get into a fight. Hirotsu orders them to cease, threatening to punish them with Falling Camellia. Aware of the severity of his ability, both Tachihara and Gin cease. Ichiyō Higuchi contacts them, and Hirotsu confirms they are ready for their mission. He's surprised to hear that their target is the Armed Detective Agency instead of the mantiger, but knows not to leave any survivors
Black Lizard arrives at the Agency's headquarters, poised for an assault. With a snap of Hirotsu's fingers, Mafiosi bust the door open, shooting a barrage of bullets at the shocked detectives. Black Lizard proceeds to make their move and attack. Despite having the element of surprise and sheer manpower, Black Lizard is overwhelmed by the Agency. Doppo Kunikida subdues Hirotsu. Some a few days later, Hirotsu and Black Lizard approach Higuchi. Hirotsu warns Higuchi to watch her step. With Akutagawa severely injured, the guerrilla squad has no real reason to obey Higuchi, as no one fears her as they do Akutagawa. He questions if Higuchi can earn Black Lizard's respect. When Higuchi insists on an unplanned solo mission to save Akutagawa from a rival group, Hirotsu urges Higuchi not to do so, as she's going behind Mori's back. Higuchi argues she can't stand around and do nothing.
Impressed by Higuchi's initiative, Hirotsu and the rest of Black Lizard later show up to help her save Akutagawa. Hirotsu comments that it's only natural for youngsters to be impulsive, mentioning that he acted out a great deal in his own youth. He explains to Higuchi that, as her subordinates, they too cannot stand by the sidelines when she's in danger.
During the Port Mafia's meeting with the Agency, Hirotsu and Black Lizard accompany Mori as bodyguards. Here, Hirotsu learns from Osamu Dazai that Mori murdered the former Boss. After the meeting, Hirotsu meets Mori in his bedroom, assuring Mori all their forces are in position for the counterattack against the Guild. He discusses the former Boss' instability and tyrannical leadership, quickly running Yokohama and the Port Mafia through the ground, and mutters under his breath the possibility of Mori never taking over. When Mori responds defensively, Hirotsu acknowledges that even Dazai must understand why Mori murdered the former Boss - as a result, he assures Mori he understands his reasoning.
After the Guild's defeat, Hirotsu meets with Dazai at a museum, noting one needs to be a certain age to understand the arts. The two reminiscences, with Hirotsu bringing up an incident of Dazai drawing a grotesque self-portrait in the executives' room that terrified Elise. Dazai praises Hirotsu's assistance. It's revealed that Hirotsu leaked the Moby Dick infiltration tactic to Higuchi upon Dazai's request - inevitably, this led to Higuchi informing Akutagawa, hence his involvement. Hirotsu asks why Dazai wanted Akutagawa to work with Atsushi. Hearing Dazai's detailed answer, Hirotsu wonders how long Dazai's been formulating this "new Twin Dark".
During the Mafia's investigation of the "Masked Assassin", Hirotsu leads Black Lizard in ambushing the assassin's hideout, only to find it empty. Hirotsu calls and informs Mori, asking if they intend to move on to the "usual plan" - Mori confirms they are. Hirotsu's unit, assigned under "siege duty", participate in the raid against the Agency after Fyodor poisons Mori. He, along with the rest of the Mafia's major Mafiosi, nearly end up in a massive battle against the detectives. However, they are all deceived by Tanizaki's Light Snow. With Tanizaki held hostage, Hirotsu, Tachihara, and Gin keep watching.
Hirotsu notes it's been ages since the Port Mafia fell to such a bloodthirsty state, and with the failed attempt of containing the virus, all possibility of a ceasefire dissolves, something the mafia knows all too well. He warns Tanizaki to brace himself, asking if he knows what happens to the Port Mafia's hostages. He reminisces on the mafia's position, stating they're not the same mafia as the one out for money or revenge. Right now, their main objective is to save their boss. Hirotsu admits he's not keen on dying for Mori, and instead intends on using Tanizaki as a spy and interrogate him. Tanizaki expresses doubts, and Hirotsu threatens Naomi Tanizaki's life if Tanizaki does not comply, claiming Gin will kill her. Tanizaki snaps, and his violent mood swings unnerve Hirotsu.
After freeing himself, Tanizaki uses his ability against the group. Hirotsu warns Tachihara not to shoot, knowing that Tanizaki's illusions mean Black Lizard may attack and injure their own. Hirotsu discovers the page from Doppo Kunikida's notebook Tanizaki hid, explaining the sudden switchblade. With the room's exits blocked, Hirotsu determines Tanizaki is serious about killing them. Tanizaki attempts to kill Gin, and Hirotsu rushes to her aid, using Falling Camellia, realizing Tanizaki used Light Snow to deceive him. With Black Lizard trapped, Hirotsu understands that Tanizaki's real target is Mori, calling Tanizaki's ability well-suited for assassination.
Whilst the war escalates, Mori manages to leave his bedroom, the mafia spread thin trying to maintain their security. Hirotsu dryly suggests contacting a detective, informing Higuchi that bodyguards watched Mori get up and leave of his own volition. Despite Higuchi's disbelief, Hirotsu muses that he understands Mori's reasoning - this is his own way of protecting the Port Mafia. After Alexander Pushkin's defeat and Mori's recovery, Hirotsu accompanies the combined forces of the Agency and Port Mafia to confront him.
Ordered to guard the Armed Detective Agency, Hirotsu attempts to dissuade Tachihara from antagonizing the detectives. He points out that, as long as the Agency stays within lines of Mori's intentions, they are not to harm them. Yosano assures him that the plan with Francis Scott Key Fitzgerald isn't a trap, which Hirotsu doubts. This is further damaged after the van Atsushi is supposed to be on explodes from a bomb.
Hirotsu orders everyone to run. During the battle with operatives, a sword impales Kenji Miyazawa, and Tanizaki is unable to remove it. Hirotsu uses his ability to force it out of the boy's body, telling the Agency to get to the mafia's secret passageway, telling them to follow him. In the lift, Hirotsum surmises that the mafia's defenses are compromised, and the Hunting Dogs' involvement will eliminate any escape route possible. He notes the Hunting Dogs' power - being superhuman ability users, and their members all being a single "one-man army". Yosano determines the Agency needs to split up for better their chances, and Hirotsu informs her that Mori's "escape plan" allows them to attempt to escape within five minutes. Hirotsu leaves the Agency to their own devices, lending them maps to navigate the secret passageways.
Black Lizard follows Yosano, saving her from an attack from a mysterious figure. Their sword aims directly for Hirotsu, who breaks it with his ability. Hirotsu tells Yosano of a getaway boat hidden in a culvert, urging her to hurry. However, the broken sword moves on its own, stabbing him. Although gravely injured, Hirotsu maintains his composure and pride, assuring the others he'll hold off their assailants. He smiles, stating that his soul forever remains with the Port Mafia. Several severe lacerations erupt upon Hirotsu's body.
It is later revealed through Tachihara's flashback that Hirotsu and Gin had survived his attack against them and had ended up being treated in the hospital for their injuries and he had gone to visit them. As Hirotsu greets Tachihara and expresses relief that he is alright and had "survived" with light injuries, Tachihara experiences intense feelings of discomfort from his comments. Gin notes the light nature of all of their injuries to which Hirotsu agrees, stating he his injuries had caused his blood to splatter dramatically, but they were all on the surface level, stating the attack only seemed like a mere "performance". As Tachihara laughs off to his comments, he jokingly slaps Hirotsu in the leg to which the latter expresses pain and snaps at him as he tries to leave the room for "another job". After Tachihara thinks about his status as a Hunting Dog and asks Hirotsu if he is suited for the Mafia, he looks to Gin in awe and begins laughing with her as Tachihara looks to them with a sorrowful look. Hirotsu expresses to Tachihara that he is surprised that he would ask such a thing and assures him that he is a "Mafia among the Mafia" and a person with qualities that are befitting of one (i.e. recklessness, bravery, and hot bloodedness) as an example that everyone should look to which Gin agrees in her silence. When Tachihara asks Hirotsu what he thinks about the Detective Agency and their innocence, Hirotsu looks to him in amazement and notes he must be more injured than they were to not know the answer. He states that anyone in the Mafia would know the answer and turns to Gin for her opinion, who answers back that there is no question that the Detective Agency are innocent as it is impossible for them to ever be terrorists. Hirotsu then tells Tachihara that as a Mafioso, he should know that as well.
- His unit, Black Lizard, refers to another piece of literature by his respective author counterpart.
- Black Lizard is also the alias of a character in a mystery work by Ranpo Edogawa.
- The painting Hirotsu and Dazai sit in front of is "Landscape", a painting by the author Osamu Dazai.