Michizō Tachihara/Synopsis

History
Tachihara details having felt like he lived in his brother's shadow. His brother was always talented and viewed as the "better" son, much to Tachihara's resentment. In order to distinguish himself from his brother, Tachihara purposely resorted to delinquency and crime. His actions led him to one day stealing from a so-called "gang", revealed to be the Hunting Dogs. He attempted to steal from them, threatened with death if he didn't join them. However much of this true or simply a cover story is unknown.

The death of his brother greatly affected his family as it did Tachihara. His family is hinted to have reacted very harshly to his death, showing disappointment in Tachihara's lack of talent compared to him and even questioned why he didn't die instead of him. This caused Tachihara to experience a strong sense of inferiority which still affects him to this day. Aware of Ōgai Mori's former connections to the military, his brother, and Akiko Yosano, Tachihara fully intended to infiltrate the Port Mafia after Ango Sakaguchi defected from his own past as a double agent.

Tachihara kept his ability a secret from the Port Mafia and rose to the rank of a Black Lizard battalion leader. The whole operation acted as a stepping stone to confronting Yosano and for the larger part, to find a way to become somebody who was "not like his brother, nor his opposite".

Port Mafia Arc
Tachihara arrives "two minutes late" to Black Lizard's meeting, their mission to attack and kill the Armed Detective Agency and kidnap Atsushi Nakajima for the bounty on his head. He mocks Ryūrō Hirotsu's strict nature, calling him a nitpicker. He points out Gin is later than him, but Gin appears behind him out of the blue. Dropping his smile, Tachihara clicks his tongue, calling her a "freak". The two almost end in a fight before Hirotsu threatens them with Falling Camellia. Reluctantly, Tachihara relents, calling Hirotsu "untouchable".

With Black Lizard assembled, Ichiyō Higuchi gives them the order to kill the Agency. The squadron easily enters the building the Agency's located in, attempting a surprise attack. Tachihara takes great glee in the attempted raid against the Agency; however, the Agency overpowers Black Lizard. Kenji Miyazawa ultimately defeats Tachihara and many others, sitting on them and later throwing them off their office.

After Ryunosuke Akutagawa's defeat after acquiring severe injuries, Tachihara joins Black Lizard in trying to dissuade Higuchi from going against Mori's orders. He comments on Gin, stating she's always receiving infiltration and assassination missions. He warns Higuchi if Gin needed to, she would've already killed Higuchi. This alludes to the risk of Mori "eliminating" Higuchi for her disobedience.

This does nothing to dissuade Higuchi, who makes her move when Akutagawa's kidnapped by an enemy organization. According to Tachihara, it was a foreign mercenary group hired by what's left of Karma, the enemy Akutagawa massacred to hijack the boat. The mercenaries are armed to the teeth, making the rescue operation too dangerous for one person. He grips Higuchi's arm to stop her, shouting that Mori will inevitably issue a rescue mission, and Higuchi should wait.

He questions what Higuchi can do on her own, but in the end, Higuchi's resolve convinces Black Lizard to assist her. They later save her life, and Tachihara orders Black Lizard's henchmen to kill anyone they don't recognize. After Higuchi and Akutagawa reconcile somewhat, Tachihara waits outside the room, smiling.

The Guild Arc
It's implied Black Lizard assisted in killing an assassin sent by the Guild alongside Chūya Nakahara and Motojirō Kajii. When Port Mafia's boss makes his entrance, Tachihara 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. Atsushi later forces him to save a baby from the chaos, much to Tachihara's confusion and reluctance. He shouts angrily at Atsushi, only upsetting the baby. Gin and Hirotsu rush to his aid at his protests, only to tease him for his flustered state, which worsens when Higuchi arrives and tries taking a photo, much to Tachihara's annoyance. They all end up scolded for "goofing around" by Chūya, after which the baby is returned to their mother by Higuchi.

Later, during Mori's and Yukichi Fukuzawa's secret meeting, Tachihara—along with the other Black Lizard leaders—act as the boss's escort detail. The group does not hesitate to try attacking Fukuzawa when tensions overflow, only to be deceived by Jun'ichirō Tanizaki's Light Snow ability.

Cannibalism Arc
With the arrival of the "masked assassin", Black Lizard gets assigned to scoping out and raiding his hideout. However, their target already fled the scene. This failure leads to Fyodor Dostoevsky's "cannibalism" scheme. Assigned to siege duty during the raid on the Agency, Tachihara and the rest of the mafia's most prominent mafiosi move in to kill Fukuzawa to save Mori's life. The group nearly ends in a massive face-off against the Agency, only to be deceived by Tanizaki's Light Snow once more. Black Lizard apprehends him and holds him hostage.

With Tanizaki hostage, Tachihara orders Tanizaki to brace himself, asking if he knows how the Port Mafia deals with hostages. Hirotsu warns him that not cooperating will end in Gin killing his sister. Naturally, Tanizaki snaps, his violent mood swings unsettling Tachihara. In retaliation, Tachihara laughs nervously, aiming his gun at Tanizaki and saying that no matter how menacing he is, Black Lizard knows his ability, assuming all he can do is "disappear".

Tanizaki points out that Tachihara is wrong, saying that he can shoot as many bullets as he wants, but a "small fry" like him can never hit Tanizaki. Tachihara takes the bait, pulling the trigger distracted by anger. This allows Tanizaki to free himself, much to Tachihara's shock. Tachihara opens fire, failing to hit Tanizaki every time. His reckless shooting nearly gets Gin killed until Hirotsu stops him.

Tachihara points out they should've patted Tanizaki down, uncertain how Tanizaki freed himself. Tanizaki almost kills Gin, until she dodges and Hirotsu comes to her aid, seemingly killing Tanizaki. Much to Tachihara's shock, however, it was another illusion, and Tanizaki has escaped.

After Alexander Pushkin's defeat and Mori's recovery, Tachihara accompanies the combined forces of the Agency and Port Mafia to confront him.

Hunting Dogs Arc
As the Armed Detective Agency is framed as the Decay of the Angel wanted for terrorism, Mori assigns the Agency's safety to Black Lizard. Tachihara vehemently protests going any further for them, as the detectives are quick to disobey Mori's orders. Chiding Tachihara for thinking like a common gangster, Hirotsu points out Mori knew the Agency wouldn't listen to him, thus why Black Lizard must protect them at all costs. With the Agency and Black Lizard working together, the plan quickly goes up in smoke when Kenji falls for a trap, which turns the tables on them.

A battle erupts between government troops against the Mafia and the Agency, during which a mysterious, hooded figure arrives. When Black Lizard and the Agency members escape to a secret lift of the Port Mafia's, Tachihara angrily rebukes the Agency's actions despite warning them that it was a trap, to which Yosano agrees. Deciding to follow Mori's escape plan, Black Lizard and the Agency split up, with the three detectives escaping separately.

For a brief moment, Atsushi and Kyōka Izumi reunite with Yosano, though they soon separate once more to bring Margaret Mitchell to safety as part of a deal with Francis Scott Key Fitzgerald. As the hooded figure catches up to Yosano and reveals the same dog tag as the soldier Yosano befriended in the past, she freezes in shock, so Gin and Tachihara come to her aid. Tachihara tries to shoot down the mysterious person, but bullets are useless. Hirotsu manages to break the sword, but it stabs him, wounding him gravely.

Tachihara forces the group to run to a getaway boat in a heavily barricaded base only the mafia has access to, assuring everyone they're safe. Yosano doubts him, and Tachihara notes how Yosano knows the mysterious figure, but she never answers. He then rigs the entrance with explosives, guaranteeing an instant death even to a Hunting Dog after them. Despite the brief respite, Yosano tells the two to leave without her. Tachihara resents the fact it seems like she's looking down on them.

He then falls into a tangent, speaking of his excellent older brother whom he hated being compared to, and states he intentionally turned to crime to avoid any comparisons with him. As he once attempted to steal from a dangerous gang, Tachihara narrates how they threateningly asked him to join their group. At the frontlines of combat, Tachihara muses how he values his superiors' orders, as they "make him who he is". Gin suddenly approaches him and stabs him without warning. With the knife controlled by an outside force, Gin is forced to stab herself as well, leaving Yosano alone with the mysterious figure once again.

A fierce battle ensues, but just when Yosano appears to get the upper hand, the explosive Tachihara put on the door doesn't work, and Yosano realizes it's a fake bomb. The figure collapses, revealed to be a metal mannequin, and the four Hunting Dogs appear before her.

Yosano realizes how the Hunting Dogs tracked the Agency down so easily in the mafia's maze, an enemy slipping in without a trace, and the fake bomb all trace back to one person. Jōno introduces the fifth Hunting Dog, and Yosano realizes the "gang" Tachihara mentioned is, in fact, the Hunting Dogs. Tachihara then reveals himself as the fifth Hunting Dog and a spy who infiltrated Port Mafia sent to monitor Mori.

Tachihara confesses that his elder brother is the man Yosano "killed" 14 years ago. When Yosano accepts his resentment, Tachihara aims his gun at her. However, he spares Yosano, and she apologizes to him for what happened with his brother, internally conflicting Tachihara.

Sky Casino Arc
Two days after leaving the Mafia, Tachihara returns to the military base to regroup with his fellow Hunting Dogs. He takes off he adhesive bandage on his nose, stating he doesn't need it anymore as a Hunting Dog. He runs into Tetchō who has been observing ants for the past 8 hours, as well as a wailing Teruko and Jōno, who praises Tachihara for all his hard work in his infiltration mission, after which he hands Tachihara back the "straight man" role to deal with their two rather unconventional teammates.

Later in the briefing room, Tachihara carries Teruko on his shoulders and briefs the latest situation regarding the Decay of the Angel, in which Atsushi and Kyōka are found infiltrating a high security bank to break out Mushitaro Oguri two days ago, after which there are no activities reported. Tachihara questions if the terrorists have already escaped overseas, to which Teruko answers otherwise, thinking that they might have found a "base" and a "command tower". After the briefing, Tachihara asks where Fukuchi has gone to; Teruko responds that he went to see Fukuzawa.

At some point, Tachihara visits Hirotsu and Gin in the hospital. Hirotsu expresses relief that Tachihara is alright, with which Gin notes the light nature of all of their injuries to which Hirotsu remarks how attack seemed like a mere performance. Tachihara laughs in response, thinking that they survived thanks to the opponent's flimsy resolve, and prepares to head out for a job.

Before leaving, Tachihara asks Hirotsu if he is suited for the Mafia, to which Hirotsu asserts that Tachihara is a shining example of a mafioso whom everyone should look to, which Gin agrees to. Shocked at his words, Tachihara admits to himself that his plan to exact vengeance for his older brother was a complete excuse, as his true reason for infiltrating the Mafia is to become someone unlike his brother nor his opposite. He then asks for their thoughts on the Agency's innocence, to which Hirotsu says anyone in the Mafia would know that it is impossible for the Agency to ever be terrorists. Hirotsu notes that Tachihara, as a fellow mafioso, should know that as well.

Once Jōno and Tetchō acquire information about Lucy's whereabouts, Tachihara and Teruko head to the Sky Casino. Along the way, he describes the history of the building and its ability to remain afloat in the sky, while Teruko recounts rumors of the casino being a hostile base, making a terrorist attack to occur to be physically and politically dangerous. They soon meet with the casino's manager, Sigma, and demands the closure of the casino to sniff out the terrorists hiding in the establishment, but Sigma refuses.

They are also threatened with the guards' directional resonance guns, with which Tachihara soon notices a shift in Teruko's personality from highly irritated to simply complying, which he understands is her scariest characteristic. Moments later, he stands in shock in the aftermath of Teruko destroying all exits to the casino as she laughs in joy. After the explosion, Tachihara walks around the casino alone searching for Atsushi and the others and any proof of terrorist activity.

He reminisces about the order Mori had given to protect the Agency at all costs and begins to think about why the Boss believes the Agency is innocent. However, he soon stops questioning the order per the Mafia's code to simply follow the Boss' order. He soon realizes his thinking in shock for thinking like a mafioso, reminding himself that he is a Hunting Dog and that his mafia infiltration is a mere mission.

After seemingly regrettably recollecting what he did to Hirotsu and Gin, Tachihara finds an odd-looking coin on the ground and also spots Atsushi sneaking by, though he fails to capture him. Lamenting that he can't find any proof of terrorism, he finds a suspicious rug on the ground and finds a hidden safe underneath, which he easily opens with his ability. As the safe opens, there are several coins from all around the world stuffed inside; upon examination, he notices they are unusually hollow with an unusual metallic structure.

The coin suddenly explodes as triggered by Sigma, though Tachihara manages to contain it by blasting the metallic fragments upwards to the ceiling. Though he survives the explosion, an unmanned plane crashes towards Tachihara's direction, unable to stop it with his ability. Teruko comes to his aid and stops the plane with her bare hands. Afterwards, Tachihara notices numerous coins falling out of the plane's side and questions in disbelief as to why Sigma would go so far to try to get rid of them.

Moments before the coins explode, Tachihara and Teruko combine their individual strengths to push the plane overboard, after which he pulls Teruko up from the explosion. He theorizes that the terrorists shall distribute the coin bombs as part of their terrorist plot; Teruko then heads out to take control of the communications room to publicize the casino's plot. They are soon surrounded by Sigma's men, but they eventually defeat all of them.

Later, a pair of casino guests attack Tachihara, learning that Sigma has placed a bounty on the Hunting Dogs. In their attempt to evade the horde of casino guests whom they cannot engage in combat with, Teruko grabs him by the collar to enact their strategy. Teruko de-ages him into a toddler and ages herself into an old woman to escape the ensuing chaos. Arriving downstairs, Teruko ages a guard and interrogates him for information on how to take control of the communications room. Afterwards, she reverts Tachihara back to his normal form as she makes way to face Sigma.

Tachihara searches for information about the terrorist's plans and finds a flash drive that Atsushi left behind, which details the Decay of the Angel' plan using a page from the Book. Teruko contacts him and asks for his findings, to which he responds breaks the flash drive and tells him that he merely found false information their targets left. Teruko then orders him to infiltrate the Mafia once more to obtain information on the two missing detectives who escaped, while the world leaders shall soon make their move.

As Teruko asks Tachihara whether he feels uneasy about the mission, he responds that he's been feeling at edge about the Mafia lately, though she retorts that he was "born to be a spy" meant for stealing, altering information, and assassinating. However, as he recalls his visit to Hirotsu and Gin, Tachihara drops the communicator and frantically believes that the Agency couldn't possibly be terrorists, making his resolve to find a way to convince the government of their innocence.

Vampire Infection Outbreak Arc
Eventually, Tachihara returns to his mafia infiltration mission and is summoned by Mori, who places his Hunting Dog cap on his head, indicating the boss's knowledge of his undercover identity. Bracing himself for the repercussions of his actions, Tachihara is surprised that Mori gladly accepts having a military police officer as his subordinate. Mori reveals having learned about it from Yosano and how Atsushi fought with and lost to the Decay of the Angel boss. With the confirmation of a mastermind, Mori appoints Tachihara as a double agent and orders him to destroy the world's enemy.

He later attends a meeting with Black Lizard and the others. To their surprise, an apparently inhuman Higuchi bites Gin. 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, instructing Tachihara to escape immediately by blasting him away. Tachihara then sees a horde of undead mafiosi and immediately escapes.

Two weeks later, Tachihara reports the incident to his fellow Hunting Dogs. Though Teruko insults how idiotic he reacted, she believes Tachihara's story, as it coincides with recent disappearances of various mafiosi. Jōno conjectures it might be terrorism using an ability, which Tetchō thinks is the Agency's next terrorist act. However, Tachihara subtly implies that the Agency cannot possibly be terrorists after recalling how the detectives kept on mentioning being falsely accused numerous times.

They turn to their commander for his approval, but Fukuchi rejects it, claiming that Tachihara's ability is needed in addressing the infection case. Nevertheless, Tachihara opens his alternative plan using the flash drive he previously broke at the Sky Casino and sending it to Deputy Commissioner Yasui, with which Fukuchi reluctantly allows him to investigate. When he also asks for the flash drive so he can hand it to Yasui himself, Tachihara gives it to him and volunteers to tell Yasui of the coming evidence.

At an abandoned location, Tachihara confronts Fukuchi after ordering Bram Stoker to bite Yasui and end the possible conflict, revealing that the flash drive he gave the commander is a tracking device. He discloses being found out by the boss upon his return to the Mafia and learns of a mastermind behind the entire incident. With his mission of destroying Kamui, Tachihara faces Fukuchi, engaging him in battle. Despite Fukuchi's skills and expertise, Tachihara gets the upper hand by controlling Fukuchi's supposedly all-powerful sword with his metal manipulation ability.

In the ensuing battle, Tachihara rids Fukuchi of Shintō Amenogozen and has him shatter his sword to drive up all the metal shards inside the commander's body, who praises Tachihara for managing to give him a challenge in battle. As Fukuchi gets incapacitated, Tachihara notices an odd "T" carved on the wall. Before he can finish questioning Fukuchi's motives for betrayal, a sword suddenly stabs Tachihara from behind.

Fukuchi explains that he used Shintō Amenogozen to cut into the past in order to leave the "T" mark to notify his self of an impending emergency. Afterwards, Fukuchi has stabbed Shintō Shintō Amenogozen into the future, which then attacks Tachihara after luring him in front of the code mark. Fukuchi also blinds Tachihara to prevent him from further using his metal manipulation ability. Tachihara urges Fukuchi to kill him rather than have him, a mafioso, begging for life.

Fukuchi enlightens Tachihara on how angels – the highest rank of beings who surpass humans and rarely suffer during their long lives – suffer 16 times worse than torture in their death, hence calling it as the "decay of angels". He likens angels to politicians, the "heavenly beings" whom others below them cannot ever reach. As such, Fukuchi, the "decay of the angels" himself, deems them worthy to die painfully and be reborn.

While Tachihara is not amused with his motive, Fukuchi brings out Bram from his coffin, telling Tachihara how their last step requires control over half of the world's nations, which Bram estimates shall be accomplished within four more days. Tachihara laughs and believes it cannot actually be possible, but he soon realizes and recalls that Fukuchi's ability can, after all, increase any weapon's efficiency by a hundredfold. As Fukuchi bids Tachihara to serve his commander again as a vampire, the mafioso slides out a blade and prepares to kill himself, but Fukuchi instantly stops him with his hands. Bram then bites him and turns him into his kind.

Some time before his encounter with Fukuchi, Tachihara turns out to have recorded himself intended for Teruko, during which he presumably contacts the Agency to acquire such recording. In his video, Tachihara voices out his trust in the Agency and asserts their innocence as a result of his investigation and despite his fears for his then incoming fate. In the final seconds, he echoes Teruko's belief that allies of justice save others even while wounded, after which he cuts off all contact.