|QUIZ TIME! Should you read any further? You might find something out you regret! Spoil at your own risk!|
July 30 (Leo)
Commander of "Black Lizard" (former)
Tachihara is a slightly imposing young man with short, spiky hair dyed rust red and amber eyes. He wears a plaster on the bridge of his nose. His natural hair colour is black.
His normal outfit consists of a long-sleeved and rather baggy white v-neck shirt with the border being black and the left sleeve rolled up so it isn't visible.
This shirt is partially covered by a military green crop jacket that has beige fur around the collar. Underneath, he wears a gun strap for his dual guns. He also wears dark blue pants, brown boots, and a black band on his left wrist.
When it is revealed that he is a member of the Hunting Dogs, he is seen wearing the standard Hunting Dogs cape and cap, but wearing his usual long-sleeved shirt, pants and his late brother's dog tag.
On the surface, Tachihara is an arrogant, impulsive, rash individual, more than willing to solve problems through sheer brute force and his dual guns. A violent temper leads to frequent conflict between him and other mafiosi, namely Gin Akutagawa, whom Tachihara views as creepy and frequently insults, leading to arguments, and Ryūrō Hirotsu, who often shuts Tachihara's temper down by threatening him. Tachihara's self-preservation prompts him to obey Hirotsu in the end, albeit reluctantly.
An apparent thirst for battle and arrogance fuels Tachihara's temper. He's often seen with a rather feral smile on his face whenever fighting. He seldom considers the weight of a mission over the rush of eliminating his targets. He shows no hesitation nor remorse in murder, in fact sometimes urging to just eliminate a troublesome person if he finds their baggage more than they're worth.
A prideful man, Tachihara despises being underestimated and belittled. This is a surefire way to get oneself shot.
His rebellious side doesn't negate how he values orders, seeing them as an utmost system. Due to this, he attempts to dissuade Ichiyō Higuchi from saving Ryunosuke Akutagawa against Mori's orders, even suggesting an alternate plan that wouldn't disobey these orders. Furthermore, he maintains his composure when dragged into shopping with Elise, and tolerates her putting bows in his hair. Despite guards laughing at him, Tachihara doesn't snap.
Despite his rough exterior, Tachihara is capable of thinking rationally, just not in the heat of the moment in the Port Mafia. He can recognise danger quickly and finds himself on edge over how nonchalant Ōgai Mori, Kōyō Ozaki, and Chūya Nakahara's meeting went. Tachihara has proficient understanding of how to deal with the enemy, alluding to a much more cunning side of his true nature.
Much of Tachihara's details of joining the Port Mafia are unknown, however, it is a ruse. His true identity as the fifth Hunting Dog reveals a much more clever, driven man. Unlike Ango Sakaguchi, Tachihara always intended to infiltrate the Port Mafia, using his position in the Hunting Dogs to operate as a spy. His confrontation with Yosano is devoid of any rage, depicting a cold, blunt side as he explains his grudge against her for "killing" his brother.
While antagonistic with mafiosi, Tachihara has a rather amicable relationship with his fellow Hunting Dogs, particularly Saigiku Jōno, who thrusts the role of "straight man" onto Tachihara upon his return. This leaves him and Jōno as the two least eccentric of the unit. Like with Elise, he's patient of Teruko Okura's spoiled personality, letting the girl sit on his shoulders with little protest of being her "slave".
What drives Tachihara is the death of his elder brother, the soldier Akiko Yosano befriended during time forced working in the Great War. Feeling he lived in his "perfect" brother's shadow during his youth, Tachihara began acting out, marking the start of his delinquency and ruthless nature. Despite his resentment towards his brother, his death deeply affected Tachihara, leading him to infiltrate the Port Mafia in hopes of one day confronting Yosano. Despite his role in watching Mori - a former military man savvy of vital information - it's unknown if Tachihara knows the greater details between Yosano, Mori, and the fate of his elder brother. To this day, Tachihara keeps his brother's dog tag.
He has an ability of an unknown name which grants him ferrokinesis, the ability to manipulate metal. It allows Tachihara to remotely control any metal object, mainly his Hunting Dogs blade and his guns. His prowess can even move a mannequin like a human, and the weapons his controls all float. 
As a Hunting Dog, Tachihara underwent intensive training and experimentation, making him physically stronger and more durable than an average human and ability user.
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 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 Tachihara. Aware of Mori's former connections to the military, his brother, and Yosano, Tachihara fully intended to infiltrate the Port Mafia after Ango defected from his own post 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.
Armed Detective Agency vs Port Mafia
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 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 united, 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 defeats Tachihara, sitting on him.
After Akutagawa's defeat and 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 organisation. 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 recognise. After Higuchi and Akutagawa reconcile somewhat, Tachihara waits outside the room, smiling.
After Yumeno Kyusaku'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, worsened when Higuchi arrives and tries taking a photo, much to Tachihara's annoyance. They all end up scolded for "goofing around" by Chūya, the baby returned to their mother by Higuchi.
Later, during Mori and Yukichi Fukuzawa's secret meeting, Tachihara —along with the other Black Lizard leaders—act as the boss's escort detail. The group did not hesitate to try attacking Fukuzawa when tensions overflowed, only to be deceived by Jun'ichirō Tanizaki's Light Snow ability.
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 Dostoyevsky'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 apprehend him and hold 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 Naomi Tanizaki. Naturally, Tanizaki snaps, his violent mood swing 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 and 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.
Despite Mori assigning 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. In fact, he urges that they just kill them, infuriated they're "looking down" on Mori. 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 fall for a trap, the explosion from the van he approaches turning the tables on them.
A battle erupts between government troops and the others, Tachihara participating. During the battle, a mysterious, hooded figure appears. Black Lizard and the Agency members escape to a secret lift of the Port Mafia's. Tachihara slams it shut, shouting that everyone knew it was a trap to begin with, to which Yosano agrees. They follow Mori's escape plan, and the Agency and Black Lizard split up.
For a brief moment, Atsushi Nakajima reunites with Yosano, heading to the real van Fitzgerald provided. However, the drivers inside are slaughtered by a sword, which floats back to the mysterious figure. It reveals the same dog tag as the soldier Yosano befriended, and Yosano freezes in shock. 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, questioning if they want Hirotsu's resolve to be in vain. He and Gin lead the detectives to 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.
Rigging the entrance with explosives, guaranteeing an "instant death" to even a Hunting Dog. 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. He states he intentionally turned to crime to avoid any comparisons, being his brother's "opposite". However, he acknowledges that acting out didn't ease his resentment. Then, one day, he attempted to steal from a dangerous "gang", caught robbing their safe. The "gang" threatened that if he didn't join them, they'd kill him.
To Tachihara, the "gang" he joined was fun. At the frontlines of combat, Tachihara didn't have to be his brother's opposite, nor live in his shadow. Because of that, Tachihara values his superiors' orders, as they "make him who he is", so if he dies for those orders, he regrets nothing.
Gin suddenly approaches him, and Tachihara mockingly asks if his story touched her. Instead, Gin stabs him without warning, and Tachihara keels over in pain. The knife controlled by an outside force, Gin is forced to stab herself as well, leaving Yosano alone with the mysterious figure once again. She looks back to Tachihara, who coughs blood in pain. Understanding the sentiment of "becoming someone" after joining a "certain organisation", Yosano resolves to protect herself and the others.
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 realises it's fake. The figure collapses, revealed to be a metal mannequin, and the Hunting Dogs appear before her.
Yosano realises 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. Saigiku begins introducing the fifth Hunting Dog, and Yosano realises the "gang" Tachihara mentioned is in fact the Hunting Dogs.
Finally returning to the scene, Tachihara arrives, revealed to be the fifth Hunting Dog and a spy that infiltrated Port Mafia in order to monitor Mori. Meaning that Hirotsu and Gin's injuries, the slaughtered drivers, and the metal mannequin were all Tachihara's doing.
Tachihara confesses that his elder brother is the man Yosano "killed" 14 years ago. According to him, the government sent him to infiltrate the mafia after Ango's fulfilled his own role. However, unlike Ango, Tachihara always intended to join. He figured that if he joined Port Mafia, he'd eventually face Yosano. When Yosano accepts his resentment, she does nothing when Tachihara aims his gun at her.
- In one of the first rough character sketches for the Black Lizard, Tachihara's black band had a smiling face on it.
- His JP voice actor, Yū Hayashi, is the singer of SCREEN mode who sung the OP theme of Bungo Stray Dogs season 2 - Reason Living.
- ↑ 1.00 1.01 1.02 1.03 1.04 1.05 1.06 1.07 1.08 1.09 1.10 Bungo Stray Dogs manga, volume 16, chapter 68
- ↑ Bungo Stray Dogs manga, volume 2, chapter 5, page 32
- ↑ Bungo Stray Dogs manga, volume 2, chapter 5, page 42
- ↑ Bungo Stray Dogs, volume 4, chapter 14, page 61
- ↑ Bungo Stray Dogs, volume 4, chapter 14, page 74
- ↑ Bungo Stray Dogs, volume 4, chapter 14, page 80
- ↑ Bungo Stray Dogs manga, volume 7, chapter 29, page 156
- ↑ Bungo Stray Dogs manga, volume 7, chapter 29, page 179
- ↑ Bungo Stray Dogs manga, volume 7, omake 7
- ↑ Bungo Stray Dogs manga, volume 8, chapter 30, page 23
- ↑ Bungo Stray Dogs manga, volume 11, chapter 46
- ↑ Bungo Stray Dogs manga, volume 12, chapter 47.5
- ↑ Bungo Stray Dogs manga, volume 12, chapter 48
- ↑ Bungo Stray Dogs manga, volume 13, chapter 51.75
- ↑ Bungo Stray Dogs manga, volume 16, chapter 66
- ↑ 16.0 16.1 Bungo Stray Dogs manga, volume 16, chapter 67