Ryūrō Hirotsu/Synopsis

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Fifteen Arc
Hirotsu is seen waiting at Suribachi City with Dazai

Dark Era Arc
Hirotsu was at the port ordering the Port Mafia grunts to clean the dead bodies at the site and orders them to look if any of the victims have families. He then notes them that one of the executives will be arriving at the site soon. Sooner later, Dazai arrived. Hirotsu reports what happened to the Port Mafia armory. While trying to finishes the report, Dazai hands him the game system which flustered Hirotsu and Dazai proceeeded to inspect the dead bodies.

After inspecting the bodies, Hirotsu was approached by Dazai and points out to cut loose any lower ranks who causes problems over narcotics. Hirotzu denies that no one of his men is involved with it. Soon afterwards, Dazai points to Hirotsu's gun. Dazai continues to reveal that one of Hirotsu's men must have caused some trouble with drugs and Hirotsu tied him up last night and stole his gun. Dazai continues to reveal what happened, and to cut the bad ones early under his command, since it's going to be a problem which left Hirotsu unable to speak. Hirotsu apologizes for what happened. However, Dazai's serious tone suddenly changed into a cheery tone, telling Hirotsu that he won't tell the boss and will leave things on his hand.

Dazai then asked if any footage of the attackers was caught. Immediately, Hirotsu signals his men and gave the surveillance picture to Dazai. Upon further checking, Dazai asked Hirotsu what gun the men at thepicture are holding. Hirotsu describes it as the grau geist. The two then discussed about the enemy organization, and learning that it's name is Mimic after one of them was captured and tortured by one of Hirotsu's men.

Armed Detective Agency vs. Port Mafia Arc
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 and sends the man flying backward with his ability. 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. 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 he accepts her order 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 Ryunosuke 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 Ōgai Mori's back. Higuchi argues she can't stand around and do nothing.

After Higuchi's meeting with Mori, Hirotsu with Gin and Tachihara confront Higuchi and warns her to stay alert and if it were him he would come up a plan before ambusing to the enemies' place. He also tells her that her and Akutagawa are the command unit directly under Mori, meaning they are Black Lizard's superiors however they don't obey her out of authorization but because of Akutagawa's ability. He then asks Higuchi what power she possesses that makes them want to obey her. Hirotsu, 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.

The Guild Arc
It's implied Black Lizard assisted in killing an assassin sent by the Guild alongside Motojirō Kajii and Chūya Nakahara. When Port Mafia's boss makes his entrance, Hirotsu promptly shows his respect.

After Q's kidnapping by the Guild, Black Lizard participates in defending their territory from further damage of Dogra Magra's widespread mania.

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; Dazai wishes to test if the two can become a new generation of Twin Dark in fighting the real disaster that lurks beneath.

In the anime, Hirotsu further asks Dazai why he cherishes Yokohama so much, to which Dazai responds that his old friend once told him to become a good man if both sides are the same. As he states how saving people has made him feel better, Hirotsu remarks and wonders if it is flawless.

Cannibalism Arc
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 Pushkin's defeat and Mori's recovery, Hirotsu accompanies the combined forces of the Agency and Port Mafia to confront him.

Decay of Angels Arc
As the Armed Detective Agency is framed as the Decay of Angels wanted for terrorism, Mori assigns the Agency's safety to Black Lizard. 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, Hirotsu 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. As his allies escape, 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.

Later on, after Akutagawa is turned through Bram Stoker's infection-type ability and infects Higuchi, the latter attends a mafia meeting and bites Gin, turning her into her kind. Hirotsu tries to attack Higuchi, only for the latter to immediately overpower him with her strength. In turn, Gin bites Hirotsu and turns him to their kind after instructing Tachihara to escape immediately by blasting him with his ability.

Plot
Hirotsu together with Tachihara arrive to escort Atsushi after their battle with the assassins. Hirotsu praises Atsushi's job in annihilating the enemies. He then immediately advises Atsushi to seek treatment from their base and tells that he can report to the boss afterwards. However, Atsushi decides to go directly to their boss leaving Hirotsu and Tachihara together with the other forces from Black Lizard.