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Yakumi Hisako (薬味久子 Yakumi Hisako?) is a character introduced in Shinyaku Toaru Majutsu no Index. A member of the Academy City Board of Directors and specializing in the medical field, she was brainwashed by Kihara Yuiitsu into having the same intellectual curiosity as hers culminating in Hisako's creation of the Agitate Halation Project.

As the architect of the project, several events prior to her introduction are indirectly caused by her. She later becomes an AIM thought being in the duration of the Agitate Halation Arc but wants to go a step further, though fails utterly and is punished severely for her efforts at the end of the story arc.


She is described as looking like a woman in her thirties. Her real age is over 70, however, her bones and organs are healthier than even those of a teenager like Tsuchimikado Motoharu due to special anti-aging treatments she has been using.[1]

She has curled brown hair that reaches below her shoulder blades, which fades into a light pinkish color at the ends. She wears a white lab coat over her lavender sweater and red mini-skirt. Her long legs are covered in black stockings which are kept up with a garter belt. Her nails are manicured as well.[1]


Her exact personality is unknown as she has been implanted with the intellectual curiosity of Kihara Yuiitsu.[2] As she was shown, she did not particularly care for Rensa's whimsical renaming of her patients, though didn't actively disallow it. She has a casual regard towards her grim profession though is brilliant in it,[1] and to her, human life was expendable if it wasn't useful to her. If they irritated her, she would send them into the darkness and if she liked them, she would miraculously save them. Either way, she took human lives lightly. She influenced them no more seriously than deciding if she wanted toast or rice for breakfast.[3] Since the pilots of Rensa are useful to her, this might be the reason why she saved them for her use.

Due to her intellectual curiosity she is apparently able to sacrifice any and all things to get what she needs, even at the expense of her own body and life, as seen when she was devoured by her own cockroaches.[4] Due to being inputted with her Yuiitsu's intellectual curiosity, she gets along well with her, much to Hisako's surprise.[2] She has no regard for immortal life without aging as nothing but a sacrilege, and looks at the value of a life in its "high score".[5] She also has the tendency to drag the pronunciation of her words.


She is a member of the Academy City Board of Directors who is influential in the medical field. She is 70 years old, though keeps her real age hidden through the use of anti-aging treatments which she acquires from her powerful connections. Not only is she influential in the medical field, she is also an expert in it, running her own hospital in School District 13, which not only acts as her home, but also as a anti-terrorism trap,[1] and a facility dedicated to the creation of new assassination techniques.[3] It is here where she based her operations for Agitate Halation and where she kept the Rensa pilot's hypothalami.[2]

At some point in the past, Hisako saved the 29th pilot of Rensa from a difficult situation which she is forever grateful for, and most likely other pilots as well.[6]

Hisako was later chosen by Yuiitsu in order for her to be used in one of her experiments. She inputted her with her intellectual curiosity via the methods similar to the ones used in the Dark May Project, and later met with Hisako, getting along with her. From then on, Yuiitsu began observing Hisako's actions due to her brainwashing, which culminated with the creation of the Agitate Halation Project.[2]

Agitate Halation Project

Main article: Agitate Halation Project

Presenting the project under the guise of eliminating the threat of "heroes" from Academy City to her fellow Board of Directors, Hisako's true purpose was to step into the realm of Aiwass and Kazakiri Hyouka, as an AIM Thought Being, and even beyond, keeping it a secret even from Rensa.[7] She apparently recruited Dr. Matsusada, Academy City's foremost expert in fluid mechanics in order for them to create the Shading Computer based on his theories of using AIM diffusion fields as its medium, knowing that it can transfer her consciousness into it. She later chooses Fremea Seivelun as the core the project, making her the target for protection for the "heroes",[8] and also, the linchpin that will hold her into Academy City once her consciousness was transferred into the Shading Computer.[7] She manipulates Skill-Out and Freshmen to inputting the necessary values to become the target for protection, the core of the experiment, artificially giving her the Agitate Halation, making her the indirect causes of the Freshmen Arc.[8] She also intended Kakine Teitoku to be influenced by the Agitate Halation, leading to the revived Kakine Teitoku's Rhinoceros Beetle after being influenced by Takitsubo Rikou's AIM Stalker ability to come to Fremea Seivelun's aid.[8] All this apparently to prove Fremea's influence in aiding the resolution the events that are surrounding them.[8]

She later notices that both Kaizumi Tsugutoshi[9] and Tsuchimikado Motoharu are investigating her project. She begins the start of the experiment in earnest, wanting to use their "heroic qualities" in eliminating the both of them in one fell swoop. She first hires a 10-man team, consisting of former subordinates of the Spider Queen, such as Anjou Haruka, Kuromatsu Takao, and Imagawa Shiguma, to kill Tsuchimikado Maika, hidden under the guise of a tool of negotiation against him as a reprisal for his investigation of the Agitate Halation Project.[10] Although, seeing the team as loose ends, she also added a Destroyer into it, most likely to hide their association with her. Moreover, she also intended to silence the Destroyer as well, and actually managed to have him assassinated using the Sniper Bee, though was too late to hide her involvement as Motoharu was able to get a confession out of him in his dying breath.[1] She most likely predicted the outcome that Motoharu would intercept the grim deed planned for her sister, and would later plan revenge after hiding her away.


Shinyaku Toaru Majutsu no Index

Agitate Halation Arc

Main article: Agitate Halation Arc

She is first seen talking to Rensa #28, flabbergasted by her tendency to nickname their patients. After noticing that the hospital has switched to emergency power, the both of them immediately recognize the potential of a threat. Hisako warns that the perpetrator may be unpredictable but Rensa keeps on reinstating that she will exterminate the intruder. Hisako then realizes that the enemy might have wanted to see which rooms went online first, allowing the intruder to bypass the labyrinthine structure of the hospital and the hidden rooms. Rensa determines that there has been an intrusion of the Critical Pathogen Specimen Freezer, to which Hisako agrees and believes that she should be evacuating just to be safe. She goes to a room in order to climb down a secret ladder leading to the underground garage, but is attacked by the Tsuchimikado Motoharu. After a moment of shock, Hisako tries to leap into the shaft where the ladder lied, but is quickly subdued by Motoharu, threatening electrocution upon her if she resisted. He tells her that she is not the one he is after but Kaizumi Tsugutoshi, apparently the one who is running Agitate Halation Project and the cause of his sister's "death". Being a member of the Board of Directors, he knows that they have ways of contacting each other. He demands her to hand it over as so to tell them that he will be coming over, and Hisako complies. Motoharu contacts them that he is coming, and leaves, taking with him the W. coccus that he stole from the Critical Pathogen Specimen Freezer.[1]

It is unknown how much Hisako predicted, but she most likely predicted that Motoharu will leak the W. coccus in his rampage against Kaizumi Tsugutoshi and Kumokawa Seria, and would swiftly eliminate the "hero" that had come to defeat him as well as per the principles of the Agitate Halation. However, what Hisako did not count were errors appearing in the project, with Motoharu, Tsugutoshi, and Seria still alive after Motoharu's defeat by Kamijou Touma, the "hero" that was summoned by Seria to defeat Motoharu.[8] Moreover, the fact that Kamijou Touma, someone that is immune to the manipulations of the AIM diffusion fields by the Shading Computer that allows the effects of Agitate Halation of the first place, came into the throng himself under his own free will was an error in itself, according to Kihara Yuiitsu.[2]

Hisako later laughs at how she survived in the "billiards game" that is the Agitate Halation Project, and notes that since she survived it means that the project is within the acceptable margins of error, disregarding Rensa's reports. After going through their "patients", Hisako tells Rensa to begin the final phase of their plan. Already finding where Fremea is located, she will be the leverage point, while Kuroyoru Umidori will be forced into being the counterbalance.[3] Essentially, it is to make the "heroes" riot by focusing on Fremea Seivelun and eventually lead them into self-destruction after killing Fremea and framing Umidori. However, the real reason would be to hide her true plans of becoming an AIM Thought Being under the Board of Directors' nose.[7]

She and Rensa later go to School District 13 to start the operation themselves. After Rensa meets and fights Umidori, Hisako notices both Kinuhata Saiai and Hamazura Shiage, and runs towards them, asking them to stop, showing the obvious fact that she doesn't run often. However, she realizes that they would be the easiest hero to draw using Fremea Seivelun (relating to the Agitate Halation). This confuses Shiage, but Hisako too realizes that words have no meaning to "heroes", and decides to try a more convincing reason for them to give up. Hisako summons her innumerable man-eating cockroaches, specifically omnivorous cockroaches. Sounds of chaos erupts of all around them. Saiai warns Shiage that they are surrounded, and there they see the cockroaches surrounding them, all under the control of Yakumi Hisako. The two are already disgusted enough but Hisako reveals that she has modified their brains to make eat anything and everything, even people.[11] The man-eating cockroaches slowly approached them. As Saiai has the Offense Armor, she is protected from the roaches, and suggests Shiage to split up with her. Shiage hesitates but Hisako cuts into their conversation, warning them that it is a dangerous gamble as though they may not be able to eat a wall of nitrogen create by her Offense Armor, but she may not able to create the wall in the first place. Saiai points out that the conditions are similar to Hisako, as she too has something that protects her and sends orders to them. Shiage tries to stop Saiai from advancing, but Saiai points out that Hisako may have the ability to attack multiple places and that they can't leave Fremea unprotected. Hisako however taunts them of even believing that they can get away, but Saiai is unperturbed. Still confident, Hisako explains the reason she chose roaches is because the disgusting image they show, causing more mental exhaustion than other insects like termites, and affecting her Personal Reality which controls Saiai's powers. The explanation alone was almost enough to overwhelm Shiage, but Saiai ignores it and tells him to run. Shiage still hesitates, but Saiai asks him if he is willing to let Fremea see the grotesque things that came from the dark side of Academy City. She reiterates that being the one that Fremea trusts is and is attached to the most, he has the obligation to live up to the trust, and that means not allowing her to see the things that the both of them have seen. With a nod, Shiage runs away from the battle, apologizing to Saiai, though she answers that she never even though he be any help.[12]

Saiai's battle concludes after Rensa's defeat at the hands of Kamijou Touma. Saiai is coated with the liquids of the dead cockroaches, specifically her Offense Armor. With countless dead roaches, countless more swarm and consume the body of Yakumi Hisako. Saiai made used of the fact that she modified the air around her by simply using nitrogen for her Offense Armor. This allows her somewhat to control air currents through tactically calling in the nitrogen for her use, and allowed Saiai to destroy the optimal layout of the "scent" Hisako used to control her roaches. Thus, the cockroaches turned on their master. However, all the while Hisako being eaten alive, she continued to smile. Saiai asks her, unnerved by this. With a laught, Hisako says that getting killed was part of her plan all along. Hisako boasts on how the plans they know of is not all of it, and scoffs at their ignorance. Saiai asks what her plan was to go so far to get herself killed like a disposable pawn, but Hisako just gives off a smug retort of asking the 7,500 "heroes" that have been summoned by Agitate Halation. Hisako "dies" with a smile, stating that the final phase is complete and the Agitate Halation Project comes into its completion. Kinuhata could not grasp when that woman had died as the roaches scatter away to parts unknown.[4]

With her body safely disposed of, her consciousness is uploaded into the AIM diffusion fields of the city via the Shading Computer. She visits the rebooted Rensa, telling her to stop being naked. After Rensa changed her skin to look like a cloth, Rensa tries to find where Hisako is talking to her but could not find her. Hisako tells her there is nothing wrong with any of her sensory organs as there is no way anyone can see her now in her current form. Hisako tells her on how she has disposed her body safely, and that her consciousness has been transferred to the shading computer that uses the AIM diffusion fields as a medium, becoming an AIM Thought Being. This surprises even Rensa, believing that the project was meant to destroy the heroes of Academy City. Hisako tells her that it was all just a ruse to hide it from the Board of Directors, and that she has now stepped into the realm of Hyouka and DRAGON (Aiwass), and that she should be able to make significant advances in her research. Hearing this, Rensa is glad and asks if she should fall back now that she has achieved her objective. Hisako however, tells that she wants to go beyond the AIM diffusion fields of the city that is used by Shading Computer, and dreams of using a different medium (a fluid) such as the winds or seas of the world, touching infinity so to speak. Rensa asks if it can really be applied to the fluids like air or water, as the reason why AIM diffusion fields was chosen as the Shading Computer's medium as it can control the students who influence each other through the AIM diffusion fields. Hisako states that it can, as humans can be influenced by the concentration of oxygen in their blood and slight adjustments in atmospheric pressure. She says that she can simply work herself into the middle of that. Rensa asks what she requires in order to shift into another medium, and Hisako responds that she needs to kill Fremea Seivelun in order to free her from the AIM diffusion fields of Academy City. Then, a vehicle arrives containing her spare parts, and asks what she has in her disposal. Hisako tells her that she can use anything but the roaches, as their guidance substance was taken they were probably gathered in once place and destroyed.[7]

The coward becomes now the hero.

For the most part of the riot of "heroes" at Learning Core, Hisako is most likely observing the events unfold before her. As Kamijou Touma battles Rensa #29 in the Lightning Rod building of Learning Core, she did not consider the possibility that Fremea Seivelun, fed up of her own helplessness and desiring to protect everyone, takes control of the Shading Computer. She is first seen laughing on how she would not be bound in Academy City any longer with the death of Fremea Seivelun. However, as she pleads for Rensa to kill Fremea already, she discovers that Fremea is looking at her directly in the eye despite being incorporeal of form. Hisako tries to deny her feelings of impending failure and continues to believe that she will succeed. And there, Fremea says that she will not hope for a hero appearing anymore. Hisako is befuddled of this, as Fremea, the pillar supporting the entire Agitate Halation Project, might cause something different if she becomes something other than a protection target. Finally, Fremea says that she will protect everyone, with that the world around Yakumi Hisako breaks apart, and Fremea Seivelun and Yakumi Hisako comes face to face. Seeing her, Hisako says that neither have any direct power, and that Fremea's death and her own escape from the city is inevitable. However, Fremea says that it is not true, for even though they are incredibly small, almost entirely useless, and even call the likes of hers Level 0, their power is not zero, there is still something they can do. With that, Hisako suddenly gains a body, despite being made of AIM, despite her body being consumed earlier, it was as if Fremea Seivelun, the core of the Agitate Halation Project, took control of the Shading Computer and, in essence, the entirety AIM diffusion fields of the City which it used as a medium. Hisako realized too late that even the weakest Level 0 can influence Shading Computer, all she needed was to realize it and Hisako gave her that realization by soaking her too deeply in Agitate Halation.[5]

Suddenly, Hisako recalls of things that she has never done nor spoken, her being kind to a child and praising humanity. Trying to deny this change overwriting of herself by Fremea using the AIM diffusion fields, Hisako begins fearing for her end. She shouts at her to wait, and tries to reason with Fremea on how grand her goal is and that she merely doesn't understand. Fremea however, tells her that she doesn't need to understand and has no interest in her project, simply wanting to have her, Hamazura's, Beetle 05's, and everyone else's smiles back.[5] Hisako is later ejected by Fremea and absorbed by Rensa's machinery, and is overwhelmed so much by it that she begins to bulge out. Hisako laughs pathetically inside of Rensa, lamenting her demise.[6] Hisako may have been completely aware of Rensa's speech to Touma, though shows no mention or care for it later, and is then forcefully ejected by Rensa from her as a final effort into saving her life from being completely destroyed by Touma's Imagine Breaker.

Hisako's AIM Thought body has been destroyed by Touma's Imagine Breaker, though she prepared insurance from it using the scent emitted by the swarm of man-eating cockroaches, transferring the medium of Shading Computer to it. She is later catapulted in a dirty back alley in School District 13 being a shallow form of her former self, being an information being forced to use the scent of the cockroaches that ate her body to continue to exist. Although she laments on how it is difficult for her now as the cockroaches have nearly been all eliminated, she is still quite optimistic of her fate, believing that she can still succeed no matter how many times it takes. She decides to restart the Agitate Halation Project, as she believes that her enemies have let their guard down now that they've won. Suddenly, Fräulein Kreutune appears before her, much to Hisakao's surprise. She summons the man-eating roaches to attack her but has not a single effect on her. Here, Hisako felt the fear of being a prey to her natural predator as she draws closer to her. She tries to convince herself that she will not be affected by any attack from her as she has no body. However, all this comes tumbling down as Fräulein somehow manages to bite and consume her. Feeling that she is gonna die, Hisako felt an odd peace, and seemingly feels as great to her as when she tried to build up her existence now that her body is disappearing. But Fräulein will not give her that satisfaction. She spares Hisako into the tiniest piece of information of her existence to survive, and tells Hisako that it is her punishment for hurting her friend, forcing her to live in a situation where she cannot die or achieve her ambitions. Finally, Fräulein with cold eyes, says that she will eat her completely if she manages to truly see herself properly, only after a long, long time.[2]

Kamijou Arc

Main article: Kamijou Arc

During the board meeting following the recovery of Academy City and reports of Aleister's death, Yakumi Hisako was referred to as an example of the board members who have been lost.[13]


Man-Eating Cockroaches

Yakumi Hisako has hundreds or even thousands of special cockroaches under her control. By applying psychosurgery and destroying specific brain cells with a neutron beam, they are made to want to eat anything and everything. As these are giant cockroaches from forests and jungles that eat wood, it means that they can also tear through flesh and bone, so they are used as a deadly weapon. Also, because they have not been genetically modified, if any of them escape and reproduce, their offspring will not have the same characteristics.[11]

Cockroaches and termites have the same evolutionary roots, yet Hisako chooses to use roaches in order to affect people's minds. That is because even if a person battles these roaches, it will eventually lead to mental exhaustion (and might affect the Personal Reality of espers as well) due to the fact most people are disgusted by roaches.[12]

Hisako controls the roaches with special microscopic scent capsules that use artificial pollen. These are prepared by taking the plasmagene the roaches use to gain resistance to insecticide by familiarizing themselves with the chemical. With two varieties of capsules, one to have them gather and one to have them disperse, she created a monitoring device to control the entire swarm, thus preventing them from assaulting her.[4]

AIM Thought Being

Main article: AIM Thought Being

Using the Agitate Halation Project, Hisako managed to elevate herself to become an existence based on the AIM Diffusion Fields of espers affected by the project, similar to Kazakiri Hyouka or Aiwass. This was achieved after her body had been devoured by her own cockroaches and her consciousness being transferred to the Shading Computer. In this form she has no physical body, yet she can still talk. As the shading computer can use any gas or liquid that can be controlled with fluid mechanics, her ultimate goal was to preserve her thought processes on the air across the entire world to be reborn as a being that far surpasses AIM Thought Beings.[7]

After being destroyed by Touma's Imagine Breaker, Hisako's existence as an AIM Thought Being was destroyed, yet she was revived in a back alley thanks to her taking insurance beforehand. Then, her existence was based on the 'scent' emitted by leftover man-eating cockroaches that she hid even from her allies. As she is no longer based on AIM diffusion fields, she refers to herself as an information life form. By turning her thoughts to words, she stabilized her existence which in turn allowed her to control the roaches' chaotic movements. Even though she no longer had any physical body, when Fräulein Kreutune found her, she managed to 'eat' Hisako's existence, eventually leaving very little of it intact. It can be presumed that her abilities and existence are severely limited due to this.[2]

Character Art Designs

Haimura Kiyotaka did not give Hisako any prominent characteristics or a deformed style, reasoning that she has no such characteristics and that she even lost her form as a human in the novel.[14]



  • Oddly enough, her hair style and clothes somewhat resemble Kiyama Harumi's. Ironically, they both have been influenced by the Kihara Family in some way, with Kiyama Harumi being influenced by Kihara Gensei, and Yakumi Hisako being utterly changed as a person by Kihara Yuiitsu.


  • (From NT7): "Physical labor is so exhausting."
  • (Hisako's unusual verbal tic, ibid): "Hee hee hee hee hee hee hee hee!! Hah hah!! Gya ha ha!! Oh, I can’t stop. I can’t, I can’t, I can’t, I can’t!! Ee hee hee ee hee! I-I can’t stop laughing! I’m dying!!"
  • (To Rensa, ibid): "There are some existences constructed from Academy City’s AIM diffusion fields. There is Kazakiri Hyouka and DRAGON. …But what if I made the scale even greater? What about the world’s oceans…no, the air. The air across the entire world. If I could preserve my giant thought processes based on its movements, I would be reborn as something that far exceeds an AIM Thought Being. What would I see once that happens?"



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Academy City Board Chairman and Board of Directors
Board Chairman
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Current Board Members
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Oyafune Monaka Kaizumi Tsugutoshi Valart Signal
Unnamed DirectorUnnamed Female Director
Former Board Chairman and Members
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Thomas Platinaburg Shiokishi Yakumi Hisako
Nakimoto Rizou (Anime).png Aleister Crowley (Anime).jpg Template Placeholder other.png
Nakimoto Rizou Aleister Crowley Neoka Norito
Three Unnamed Directors
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Yoshikawa.jpg Amai Ao.png Kiyama Harumi1.jpg Nunotaba shinobu.png
Yoshikawa Kikyou Amai Ao Kiyama Harumi Nunotaba Shinobu
Keitz Nokleben (Anime).png KusakabeYumi profile.jpg KanmiEiga profile.jpg Makuwa (Anime).png
Keitz Nokleben Kusakabe Yumi Kanmi Eiga Makuwa
Hishigata Mikihiko (Anime).png Go Hazime.PNG Kuriba Ryouko After Experiment (Anime).png Chief (Anime).png
Hishigata Mikihiko Go Hazime Kuriba Ryouko Chief
Female Scientist (Anime).png Toomine face.png Scarred Doctor Profile.jpg Yakumi.jpg
Female Researcher Toomine Kanari Houjou Seigo Yakumi Hisako
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Sarizawa Saya Kasasagi Garan Kyouji Usui Yoshino
See also: Kihara Family
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AIM Beings
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Kazakiri Hyouka Aiwass AIM Burst Yakumi Hisako