Akiko Yosano/Synopsis

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History
Fourteen years ago, Yosano, only 11, acted under a military medical scholarship alongside their first-class assistant physician, Ōgai Mori. The two worked on the medical unit for a military troop stationed on Tsukoyami Island, a mysterious location where night prevailed.

Yosano, constantly exposed to death and trauma, used her ability to heal soldiers, all of which were deeply grateful for her saving their lives. Yosano disliked them holding her up on a pedestal, and often spoke harshly to them, maintaining her usual tough personality. Despite the troop's respect of her, they suffered Mori's possessive nature over her, often threatened by him with a gun, with no doubts in their mind he'd kill them. Yosano explicitly stated she's not his property. Mori reasons that he's still her superior, and he has every right to correct her attitude. Yosano disagrees, stating she knows nothing of military protocol, revealing that just last week, she'd worked in a confectionery store until Mori forcibly drafted her into the war.

Yosano notices one of the healed soldiers reading, questioning how he could be reading a novel after being half-dead earlier. The man corrects her, saying it's a poetry book. Disinterested, Yosano says she wouldn't make him thank her, instead of ridiculing him for not returning to the front lines after getting injured. The soldier assures her he's thankful, summoning a butterfly that forms into a golden hairpin in her hair. The soldier thanks her, calling her "Miss Angel", which flusters her greatly. Yosano asks him if he used an ability, which he confirms, but says it's nothing like Yosano's, which he believes could change the world. Yosano disagrees, but the man says that's because she's a foot soldier without an outside perspective. According to him, European forces already learned those ability users will turn tables in times of war, and Japan rushed to match those expectations in order to not fall behind, determining that's why Mori made Yosano join the war, asking Mori if he's correct. This displeases Mori, as his essay to the emperor, "An Immortal Regiment", should've been confidential. Listening to them Yosano understands nothing, having assumed she just joined to save lives, but Mori forces her to leave the man and tend to the next wave of patients.

After another devastating defeat, the troop returns, fatally injured once more, the man included, having lost his arm. However, he wakes up completely intact, with Yosano staring with empty eyes at him, covered in blood. Exhausted, Yosano reveals she healed 80 people at once. She's realized that, although she can heal bodies, she can't heal the psychological damage and trauma, recalling a man with his torso blown off. Even though he's physically fine, he can't even say his own name now. She tells the man the ones alive returned to the battlefield, as they're short on manpower.

Yosano asked the man what an angel is, as she felt it's just someone who heals so people can die again. The man disagreed, and reveals the back of his dog tag, with tally marks on it, recording how many times she's saved his life. This incident marked five times, so the tallies make the word "correct", comparing the "correctness" of five tallies to Yosano's own "correctness", revealing that without her, he'd never be able to see his family again. He said he's glad Yosano's here, making her cry and thank him.

Another soldier ordered the man they need more manpower, and he ran off to help.The war goes on, getting worse and worse. Yosano had to heal more often, to the point of two or three times in a single day. Whereas a normal army would've retreated, the Infantry didn't, because it had Yosano to make use of.

Armed Detective Agency vs. Port Mafia Arc
She, among the other ability users of the Armed Detective Agency, was present the night Dazai revealed Atsushi to be the man-eating tiger. She later expressed disappointment at the situation by stating that the lack of casualties was "boring". When Dazai decides to have Atsushi join, she shares the others' surprise in his decision.

Later, Yosano is during Black Lizard's assault on the Agency. Whilst Kunikida and Kenji Miyazawa fend the Mafiosi off, Yosano sits down, nonchalantly drinking tea and chatting with Ranpo Edogawa. She does, however, assist Kenji in tossing Mafiosi out the window. And later assists in repairing the Agency's office.

The next day, Yosano later arrives, complaining about oversleeping, greeting Atsushi, and asking offhand if he has any injuries, much to her disappointment when he says no. Yosano decides to have Atsushi help to carry bags whilst shopping because he's the only one in the office (after everyone ran off thanks to Ranpo's warning). After forcing him to come along with her, Yosano makes him carry the numerous packages that she bought, warning him to not drop a single one. Atsushi asks what'll happen if he does, and Yosano turns to him with a menacing smile.

Atsushi, occupied by a passing girl, bumps into a man, dropping the boxes he was carrying and knocking the man to the ground. The man immediately goes off on Atsushi for dirtying his expensive suit. Yosano, seeking to defuse the situation, apologizes and wiped the man's suit, asking if he was hurt. Instead of calming down, the man kicks Yosano away and proceeded to criticize her in a lewd and derogatory way. This causes her to lose her patience and hurtfully grab the man's hand. She mocks him, the sadistic smile returning, asking if she should crush 'something' under her heel instead, terrifying both the man and Atsushi.

At the train going back, Atsushi apologizes for the situation he caused earlier and for dropping her things. Yosano tells him not to worry, and suddenly examined Atsushi's leg, which was torn off by Ryunosuke Akutagawa's ability. Finding no trace of the injury, she marvels it—musing that what happened to Atsushi was a full restoration instead of a mere regeneration. After letting go of his leg, she explains that it's a shame she didn't get to treat him. Yosano then warns Atsushi he won't be so lucky next time, as the Port Mafia is known for their surprise attacks, and he's their target.

Right at that moment, the train's PA system sounds. A man claiming to be the train's conductor apologizes for the inconvenience, as he intends to conduct a physics experiment. An explosion follows his explanation, killing several passengers. The man then orders Atsushi to hand himself over, threatening to kill everyone aboard the bomb rigged train should he fail to do so. Yosano gives Atsushi three options: turn himself in, leap off a running train with all the passengers, or defeat the enemy. Atsushi chooses the latter, and Yosano gives an approving smile, as this is what the Agency is all about. Just before they can get down to business, the rude man from earlier interrupts them. He orders Yosano to hurry and save him, and Yosano smugly retorts that the Agency isn't a charity. The man starts begging, and Yosano agrees. However, he interrupts once more, now bashful and asking if she meant her threat from earlier. Angered and disgusted, Yosano knocks him out by slamming his head on the floor.

She and Atsushi split up to defuse the bombs, and tells Atsushi to tear the enemy apart should they run into them. Calmly making her way through panicked passengers, smiling, Yosano muses on the Port Mafia's attack. It's uncharacteristic of the Mafia to see through with an attack in broad daylight and major fallout in its wake. She determines that's how set they are on obtaining Atsushi, and wonders who could be behind the scheme. Opening the door to the next car, she steps on a lemon-shaped bomb, its ring caught on her heel. It detonates, knocking Yosano over. The bomber reveals himself, assuming she died. Yosano regains her footing, however, noting how she didn't expect to run into a 'celebrity'. The bomber praises her resilience, and Yosano notes the man's public appearance is more of a surprise. She states she knows exactly who he is, the terrorist Motojirō Kajii.

Motojirō goes on his tangent of death as an experiment, angering Yosano, and she challenges him to try and find out the color of her blood. During the fight, Motojirō uses several bombs against her, weakening her greatly. Yosano tries to move, but Motojirō stomps on her stomach, mocking her, and asks her what "dying" is exactly. Yosano's eyes widen at the question, but Motojirō presses her. Stating that death can be "reversed" easily in a lab, but questions death's imminent nature. The question makes Yosano laugh, and she mocks him for being an idiot. Motojirō snaps and stabs her hand, surrounding her with lemon bombs, and leaves the car. Yosano struggles to get the knife out her hand but fails, and the bombs detonate.

Motojirō returns to see his handiwork, finding Yosano's body slumped over an open window. When he goes to inspect it, Yosano immediately punches him in the face hard enough to send him flying against the wall. Unsatisfied with the punch, Yosano asks if Motojirō really thought those "sprinklers" would kill her, and asks which side of his face she hit. She hits the other side, sending him flying again. She introduces herself as a doctor, one who's seen far more death than he has. She answers his question, stating death as "the loss of life". As a doctor, she's witnessed patients die right in front of her no matter the attempt. She threatens Motojirō, stating anyone with such little regard for life will die by her hand.

She explains the workings behind Thou Shalt Not Die, a rare ability capable of healing all external wounds, hers included. However, she has to half-kill victims with non-fatal wounds before treating them. Upon saying this, she rummages through her medical bag, pulling out a large cleaver. Observing Motojirō wounds, Yosano gives another sadistic smile, "offering" to "fix him up". She uses her ability to force Motojirō to cooperate in interrogation. Afterward, she uses the P.A. system to contact Atsushi, informing him that the bomb is on Kyōka Izumi. Yosano later sees Atsushi jump off the train to save the girl, calling out for him in concern.

Yosano keeps watch over Kyōka when the Agency recovers her, and informs Atsushi and Kunikida when she wakes up.

Later, she is seen attending the meeting to find Atsushi after the Mafia abducts him, but doesn't accompany Kunikida to save him. After Atsushi defeats Akutagawa and ultimately saves Kyōka, Yosano joins in on playing dress-up with her, welcoming her with open arms to the Agency.

The Guild Arc
After the Guild's attack on Atsushi and the others, Yosano heals them all. She straps Atsushi down to an operation table, revving up a chainsaw. Excited, she happily announces it's time for Atsushi's treatment. With everyone healed and traumatized from her treatment, she offers no sympathy for them, stating they'd be six feet under without Thou Shalt Not Die. When Atsushi tries to follow the President on his way out, Yosano discourages him, saying Fukuzawa is too riled up for a company.

The Agency goes into hiding at a secret base, strategizing against the Guild and Mafia. A defense team includes Yosano, and it's the team's main objective to keep her safe, as there's no hope of winning without her ability to save their lives if need be.

Yosano assists in watching surveillance of the tunnel leading to their base, commenting that's things are more boring than anything. Yosano agrees, noting that the several traps set up will make someone second guess invading the tunnel. In his own boredom, Ranpo challenges her to a game of hanafuda, and she eagerly accepts, asking what the stakes are this time.

However, Ranpo notices something amiss on the surveillance - Chūya Nakahara infiltrated it. Yosano shares the Agency's disbelief at how effortlessly Chūya dismantles their surveillance and gunfire, and Fukuzawa sends both her and Kenji out to confront him. Yosano tells him the Agency has a strict "no walk-ins" policy, ordering him to bother someone else. However, she agrees that if he wants to bust in, he can, but the Agency is aware that's not what he's here to do. She directs Chūya to a camera where he communicates with Fukuzawa from, where Chūya explains the Mafia's set-up, having leaked Guild members' whereabouts to the Agency for them to take care of.

Yosano admits it's a tempting offer, but states she has a better one. She points her cleaver at Chūya, suggesting she sever all his limbs and force him to confess what the Mafia's really after, with Kenji joining her. Yosano attempts to hack him from behind, but Chūya avoids her, now standing on the ceiling. Yosano realizes who he is and his identity, annoyed at him and yelling at him to get down. Chūya obliges, destroying much of the area around him, save a pillar where he stands, but to Yosano and Kenji's shock. Chūya challenges them to defy gravity, and Yosano's expression makes it clear she and Kenji are no match against him.

After the Guild captures Q and unleashes Dogra Magra upon Yokohama, Yosano participates in guarding and watching an afflicted Kunikida.

When the Guild receives a challenge from one of its members, Yosano accompanies Ranpo to confront the one behind it, commenting that the "invitation to a deduction game" is likely a trap. They reach the room, meeting Edgar Allan Poe. She's shocked to hear that Poe is willing to reveal Moby Dick's weaknesses if Ranpo beats his challenge. She continues to deduce that this is a trap even after Ranpo agrees to it, but Poe invites her to participate as well.

Yosano proceeds to read the mystery with Ranpo, sucked into the book's world by Poe's ability, appearing in a different room from Ranpo, and in a traditional doctor's uniform. She finds him with the body, rushing to save the victim, who's alive enough to point out a door in the room. In the aftermath, Yosano comments on the creepy realism of Poe's ability, noting that her ability doesn't work in it. She sums up the murder, the victim being the mansion's manager, the murder weapon having no fingerprints, and Ranpo confirms it as an 'impossible crime'.

Noticing Ranpo's poor demeanor despite knowing the ins and outs of the crime, questioning why he doesn't use Ultra Deduction to solve the mystery. Ranpo points out he doesn't have his glasses, required to "activate" his ability, which wouldn't work anyway given that Yosano can't use hers either. Aware Ranpo has no ability, Yosano plays along, suggesting they solve the crime through normals means. Unfortunately, this greatly displeases Ranpo, who detests the tedium behind normal investigative methods.

Left with no choice, Yosano leads the investigation, gathering the mansion's other four guests to interrogate them, asking their alibis. The woman of the guests refuses to cooperate, insulting Yosano as a mere house doctor. Yosano stabs the table with a scalpel, intimidating her. The guest cooperates, claiming to be in the manager's room for a change in clothes, thirty minutes before his death. The guests begin to theorize and argue, thinning out Ranpo's patience. He snaps and corrects them on the case's true details and reaches his own conclusion, and Yosano praises him but conflicted Ranpo storms off.

Yosano follows him, pointing out Ranpo already knows his skills aren't an ability. In denial, Ranpo questions if Fukuzawa lied to him. Knowing how much Fukuzawa means to Ranpo, Yosano doesn't push him. She leaves him be, returning to her room, locking it, using an ax for protection, knowing the serial murders will continue. Although seemingly prepared, Yosano overhears a strange noise, attacked by an unseen assailant. The guests and Ranpo crowd in her room, finding Yosano with the ax in her abdomen.

She apologizes to Ranpo, saying she messed up and can't solve the case herself. However, she's certain Ranpo can, seeing as the forming of the Agency happened to give Ranpo a place he belonged and could make use of his skill. Dying, Yosano says that, to this day, she's grateful Ranpo invited her to the Agency. Her glasses fall off, and Ranpo uses them. Ranpo solves the mystery, freeing himself and Yosano in time for Yosano to use her ability, and defeats Poe. They depart with Moby Dick's documents. Yosano suggests they celebrate to commemorate the day Ranpo realizes he has no ability. Ranpo refuses, telling Yosano not to make an ordinary person out of him after all this time. Although surprised, Yosano smiles and laughs, with Ranpo telling her not to laugh or sass him.

Later, Yosano is among the other Agency members who proudly witness Kyōka pass her entrance exam. After the Guild's defeat, Yosano joins in for Kyōka's welcoming party, enjoying herself drinking. She approaches Kunikida, loudly complaining that everyone's too much a lightweight to enjoy drinking with her, telling him to join her, and reminds her he has something to say to Atsushi and Kyōka.

The Guild Aftermath Arc
Yosano attends a group-gathering at the cafe, only to find it trashed and its employees badly hurt. Participating in the assault against Zoopark, the group responsible, she gives a wicked smile, noting the group leader's tendency of tearing off fingernails.

During a day she wants to shop, Yosano invites Kunikida along, but he declines, busy with his own schedule. However, after Kunikida's own outing results in him being in danger, he bides his time until Yosano can reach him, and she saves his and Aya Koda's lives.

Cannibalism Arc
Yosano looks after Fukuzawa after getting afflicted with a virus and later discovers a mysterious seal on him from it. She confirms that it's sucking away his life force and that he won't last much longer. She informs everyone Ranpo's staying with the President, shaken up by his condition. When Ranpo recovers after the Port Mafia surrounds the building, she asks if he's okay. Ranpo encourages them, especially asking Kunikida as their interim director to issue his comrades with his orders. As such, Yosano and the rest of the Agency simultaneously guard Fukuzawa's room.

As they face off with the mafia's main forces led by Chūya, Yosano and the others begin to dissipate, revealing it as Jun'ichirō Tanizaki's illusion. In truth, Kenji had blasted through the wall and carried the President out to safety with the others, rethinking their strategy in their escape. Later, Yosano and Ranpo regroup with Atsushi and the caught man, who relays Fyodor's message that the rules cannot be changed.

Later, Yosano, Tanizaki, and Kenji proceed to go to the Port Mafia headquarters in attempt to fight the mafia. After arriving at the enemy's headquarters, they are constantly being attacked. After a while, they hear that the gunshots have stopped only to find out that Motojirō carries a huge number of lemon bombs causing the place to explode. Yosano tells Tanizaki and Kenji that Motojirō is a walking bomb, and if they both got any closer, it would be difficult to even heal them both. Yosano then commands them to retreat.

After fleeing from Motojirō's Lemon Runway, Yosano with Kyōka, Tanizaki, and Kenji go back to the Agency office. While tending to Kyōka's injuries, she later receives a call stating that Fukuzawa left Lucy Maud Montgomery's room. After Pushkin's defeat, Yosano is together with both the Agency and the mafia to confront him.

In the anime, Yosano attends a banquet held by the Agency at a luxury liner given to them by Francis Scott Key Fitzgerald. Kunikida apologizes to Fukuzawa on the Agency's behalf, willing to accept their punishment for disobeying the President's order not to fight the mafia. Nonetheless, the President smiles at them and is grateful for their efforts.

Decay of Angels Arc
The Agency receives word of a "murder association", the Decay of Angels, and later receives a hostage situation stream from one its members - Nikolai Gogol. He challenges them to save the hostages in 30 minutes without help from the government, otherwise, the hostages die. However, the military arrives on the scene before the Agency, forcing the Agency to prevent their entry.

The Agency infiltrates the building, outside the hostages' room, prepped to save the hostages. However, when Gogol orders henchmen to remove their hoods, the chainsaws slaughter the hostages. Hearing the screams, the Agency burst in, but the Agency appears in the room wearing the henchmen's clothing, being the ones removing their hoods. Right at the same time as the military bursting in to ascertain the true culprits. As a result, the Agency is framed as the Decay of Angels.

A sniper attempts to kill Kunikida, but Yosano shield him, wounding her shoulder. The Agency attempt to escape, barricading a room, but the military shoots the room with a sleeping gas dart.

Forced to drastic measures, they all commit suicide, sans Yosano. Yosano greets them, using the 'fourfold' extend of her ability to revive everyone. The Agency defeats the military troop, escaping the building.

Escaping to the forest, the Agency tries to gain their bearings. Yosano notes how that life isn't a fairy tale where the hero saves the country, instead the military is the most powerful. Kenji, however, ends everyone's pessimism, calling this "storm" and "blessed rain" the same thing, and that they'll get through it no matter what. The group discusses their next course of action, but their plans coincide directly with the Hunting Dogs. Nonetheless, Yosano praises Kunkida's first priority being innocent bystanders' safety, and tells them to head out.

After hijacking a car, the Agency proceeds with their plan. Yosano tells Kunikida to floor it, but admits it's like him to obey speed limits even now. For now, their main priority is to find a safe place to hide. Yosano knows of one, but hesitates bringing it up. Jōno suddenly appears in their car, and the group is forced to escape. After deterring Jōno and Tetchō, they almost escape, but Tetchō's ability slashes the car in half.

Yosano tries to use her ability to heal herself, but the two Hunting Dogs return, and before anyone can defend themselves, Tetchō severely injures Tanizaki and Kenji, and slashes Kunikida's notebook in half, rendering his ability useless. With them unarmed and hurt, Jōno orders Tetchō to kill Yosano, calling her the "Angel of Death", and that killing her is for the worlds sake. Shocked, Yosano asks why he knows that name.

Kunikida begs them not to kill her, but just before Tetchō can, Chūya arrives in a helicopter. He throws bullets, using his ability to propel them and shoot the swordsman's shoulder. Chūya retrieves them on the helicopter, informing them that the only reason he did so was that Mori and Fukuzawa agreed to have the Mafia recover the Agency, so long as one of their members went to the Mafia in exchange.

However, Tetchō attacks the helicopter. With no other choice, Kunikida sacrifices himself to stop Tetchō, leaving Yosano and the others worried for his well-being when he summons a bomb.When the group reaches the base, Yosano's seen, exhausted and worried for everyone's well-being.

Mori informs the Agency his plan of having the group split up and sent away, which infuriates Yosano. She asks what else they're supposed to do, but Mori says they can do nothing but stay quiet and hide. Yosano grips his shirt, saying she always knew he had no intention of helping the Agency. She knows Mori has no interest in transferring just anyone to the Mafia, knowing it's her that he wants.

Mori tells her Fukuzawa already agreed to the deal, but Yosano refuses to believe Fukuzawa would. However, Mori tells her Fukuzawa himself said he could choose her, to Yosano's great shock. When Francis Scott Key Fitzgerald contacts the Mafia for a meeting and a deal, Yosano attempts to leave and go through with the deal, aware it's likely a trap. Tanizaki and Kenji stop her, and Tanizaki offers to go to the Mafia in her stead. He asks Yosano why she hates Mori so much, and asks if it's connected to her title as an "Angel of Death". Yosano confirms his suspicions, telling him he doesn't need to go so far for her sake, agreeing to tell him what happened between her and Mori.

Plot
Yosano, with Kenji arrive in the middle of the agency members' request to Ranpo in helping finding Akutagawa's sister.

Later during Akutagawa's need of the agency members' stamp of approval, it was revealed that Yosano's request is to heal Akutagawa 40 times.

After Akutagawa's fight with one of the Port Mafia member, Atsushi Nakajima, she treats Akutagawa's injuries. She then gives him the card with everyone's stamp of approval and informs him upon waking up to follow her and will show something to him. The two go to the conference room and see the other agency members sitting.