166 cm (5'5")
Flowers, eels, sake,
Male chauvinism, weak men
Thou Shalt Not Die
Kimi Shinitamō Koto Nakare
Yosano is a young woman who takes care of her appearance. She has black hair with straight bangs cut into a bob that reaches past her chin. In the manga she has dark grey eyes, which was changed to pink in the anime.
She wears a white button up blouse with puffy sleeves that end in the middle of her forearm. Her shirt is tucked into a plain black skirt that flares out above the knee. She wears gloves that reach past her wrist, a black tie, and black tights. Yosano wears red high heels and a golden butterfly hairpin on the left side of her hair.
Yosano is a lady who carries herself with utmost grace and dignity. She prides herself in being both a strong woman and a capable doctor, which is why she does not take too kindly to those who belittle her in both respects. She appears to be a feminist who believes now is the age of equal rights for men and women. She almost always depicted as calm and composed, but when angered, she is quite the force to contend with.
Despite her appearances, she has shown prominent sadistic and aggressive tendencies, which is more so magnified by her ability's conditions. As a result, most members from the Agency flee when in her presence and as much as possible, avoid getting injured even in the slightest so as to circumvent her unique brand of “treatment”.
As the sole doctor of the Detective Agency, she highly values human life and is significantly averse to meaningless deaths and killings. She will violently admonish those who believe otherwise and is very keen on doing so without much hesitation.
On a side note, she appears to love shopping to a great extent, and when not working is often showing buying large amounts of clothes such as in episode 8 and chapter 40. This could also imply she is a fashion conscious.
Yosano has a rare ability among ability users, Thou Shalt Not Die (君死給勿, Kimi Shinitamō Koto Nakare?), which allows her to heal external wounds. However, to heal someone they must first be "half-dead"; meaning they must have fatally serious injuries before she can use her ability. Due to this, her ability is inconvenient for healing minimal wounds since she needs to fatally injure that person first.
She is also quite skilled in close combat, showing proficiency in wielding a large cleaver that she occasionally uses, as well as enough skill in unarmed combat to defeat members of the Black Lizard easily.
She was one of the people who attended the meeting Dazai organized to think up Atsushi's entrance exam. In chapter 32, it is revealed Rampo is the one who invited her into the detective agency in the first place.
She, among the other Ability Users of the Armed Detective Company, were present the night Osamu Dazai revealed Atsushi Nakajima to be the man-eating tiger. She later expressed disappointment at the situation by stating that the lack of casualties was "boring".
The Tragedy of The Fatalist
Teaching Them To Kill; Then To Die
Looking for a shopping partner, Yosano decided to take Atsushi with her as the remaining members of the agency had flown the moment they realized her intentions. After forcing him to come along with her, Yosano made him carry the numerous packages that she bought, warning him to not drop a single one.
Atsushi, occupied by a passing Kyouka, bumped into a man, dropping the boxes he was carrying and knocking the man to the ground. The man immediately went off on Atsushi for dirtying his expensive suit. Yosano, seeking to defuse the situation, apologized and wiped the man's suit, asking if he was hurt.
Instead of calming down, the man slapped Yosano's hand 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 then says that she's a doctor, and threatens to cut off his body parts because he seems to have too many.
At the train going back, Atsushi apologized for the situation he had caused earlier and for dropping her things. Yosano told him there was nothing to be sorry about, and suddenly examined Atsushi's leg, which was torn off by Ryunosuke Akutagawa's Rashoumon. Finding no trace of the injury, she marveled at it—musing that what happened to Atsushi was a full restoration instead of a mere regeneration. After letting go of his leg, she explained that she was sad she didn't get to treat him. Yosano then warns Atsushi to be careful, as the Mafia were known for their surprise attacks and he was their target.
Right on that moment, the train's PA system sounds. A man claiming to be the train's conductor apologized for the inconvenience, as he was going to conduct a physics experiment. His announcement was then followed by an explosion which killed several of the train's passengers. The man then ordered Atsushi to hand himself over, threatening to kill everyone aboard the bomb rigged train should he fail to do so, Yosano ordered Atsushi to split up and look for the bombs, with her taking the front side of the train.
The moment she opened the door to the next car however, she was immediately injured by the explosion of a lemon shaped bomb. The bomber was revealed to be none other than the famous Mafia operative, Motojirou Kajii. Not given time to prepare herself, Yosano was quickly subdued by Motojirou. Before moving to kill her, he asked her the reason as to why all humans must die. In response to this, Yosano mocked him, saying that he is an idiot for not knowing such a thing. Enraged, Motojirou stabbed her hand, effectively preventing her from getting up from the floor. He then surrounds her with bombs which exploded shortly after her left the train wagon Yosano was in.
After a while, Motojirou returned to examine Yosano's body. To his surprise, she was completely uninjured, with her tattered clothing as the only proof that the explosions had ever happened. Yosano proceeded to send him flying with a punch to his face. She disagreed with Motojirou's view that death was the ultimate form of science, saying that it is the loss of a life. She claimed that she had seen at least a hundred times more deaths than he had, and will kill anyone who does not value life.
Yosano went ahead to explain her ability, stating that it can heal any external injuries however under the condition that it is fatal. Therefore, in order to use her ability to treat her patients, she must first mortally wound them. While taking out a blade from her bag, she observed that Motojirou was injured, and asked if he wanted to be treated by her. Not waiting for a response, she proceeded to brutally hack at Motojirou.
After healing Motojirou to a flawless state, Yosano used the train's PA system to tell Atsushi that the bomb had a remote detonator, and he could use the stop button on it to defuse the bomb.
- She made an appearance along with several other characters in the mobile game "Kimito Lead Puzzle 18" as a limited time character.
- Yosano is named after a feminist pacifist poet whose work was considered controversial in her time for portraying and encouraging female sexuality. Her ability is likewise named after one of the real Yosano Akiko's poems, which was addressed to her brother and published during the height of the Russo-Japanese war. It was subsequently made into a song and sung in protest to the war.
- She says the obituary is the most interesting section of the newspaper, as it judges people "the most fairly," to which Dazai agrees.
- Yosano reveals that she and Mori had a connection long ago. This also applies to their real life counterparts, as Mori assisted her in finding travels outside Japan; Yosano was a member of one of Mori's poetry groups and also asked him to name her twin daughters.