The Hinamizawa Syndrome (雛見沢症候群, Hinamizawa Shōkōgun) is an organic brain disease found in people who have lived in Hinamizawa of uncertain etiology for much of the series. It appears caused by a type of parasite which can only be recovered from living tissue. How inhabitants and visitors acquire it remains unknown. The parasite appears quiescent until triggered, usually by the infected leaving the region. The signs and symptoms of the Syndrome include the development of anxiety and paranoia accompanied by delusions which can lead the sufferer to commit seemingly unprovoked violent acts including suicide and murder, and the sensation of insects crawling under their skin, the real symptom known as formication. This leads to a classic sign of clawing at the skin, especially over the involved lymph nodes of the throat. Victims in the end-stages may claw out their own throat.
Dr. Takano's Report on Hinamizawa Syndrome
According to Matsuribayashi-hen, Dr. Takano had already discovered the existence of Hinamizawa Syndrome about 20 years prior to the story. He wrote a report regarding the town and its disease plaguing its residents and called it Hinamizawa Syndrome. His goal was to securing funds for its research, eventual treatment, and increasing the awareness of the general public. However, Dr. Takano encounters real political opposition. Dr. Takano learned that one of the soldiers from the Japanese garrison in Manchuria came from Hinamizawa, likely suffered from the disease, and may have fired on the Chinese soldiers on the bridge which initiated the infamous Marco Polo Bridge Incident. Both China and Japan blame the other side for firing first and subsequently triggering the bloody Second Sino-Japanese War; Higher officials cannot accept his report since to do so would require Japanese acceptance of the blame for the Incident, and China would likely use this information as political and moral leverage against Japan. Further, this would require the Japanese government to essentially accept Japanese blame for the start of a war that ultimately led to the WWII, hence the cover-up. After Dr. Takano's death, his adopted granddaughter Takano Miyo takes over the research on Hinamizawa Syndrome. She receives funds initially from Koizumi, a former superior of Dr. Takano, who felt guilty over betraying him and helping to suppress his research. After his death she then receives funding and support from a mysterious woman named Nomura who represents a faction called "Tokyo". With Koizumi's death and lessening of his faction's power, supporters of Takano suddenly turn on her. They ridicule the research they previously praise and order the infection eradicated and the matter suppressed. Facing the end to her research, and with the support of Nomura, Takano decides to trigger a village-wide outbreak of the Syndrome, or at least make it appear that one is happening, to justify the initiation of Emergency Manual #34 to trigger the Great Hinamizawa Disaster.
The entire series, from the visual novels to their manga and anime adaptations, never full clarify the full orgins and nature of the disease. Details come out as clues which may appear contradictory given the character's knowledge and the respective arc. For example, Takano and her supporters become convinced that Furude Rika acts as a "Queen Carrier" who suppresses the Syndrome from developing in all of the Hinamizawa residents; however, in arcs where Rika dies at the hand of Shion the Syndrome does not develop.
Further research in the Irie Institution
While appearing as a village clinic, the Irie Clinic is actually an institution complete with secret underground facilities devoted to research into the Hinamizawa Syndrome. The research that takes place is based off of the collective data of the roughly 2,000 villagers and Dr. Takano's research in the military. Dr. Takano found evidence that a brain "parasite" is responsible; Takano and Irie Kyōsuke confirm the presence of a parasite that abandons/disappears from its host as soon as the host dies. The exact nature of the "parasite" and its origins is never fully revealed. This ties into some of the stories and legends concerning Furude Hanyū: that it was a "sickness" that came about the time her "people" arrived that they could help treat. The legends run the gamut from the supernatural--Hanyū is a demon who becomes a locative goddess--to the extra-terrestrial--Hanyū is an alien who becomes a locative goddess. Readers should take solace that the series does not intend to answer everything, and Rika later admits to Hanyū that over the 100-odd years of existence together, no matter how many times Hanyū has explained her origins and existence, Rika still cannot understand it!
Some things do become clear. To begin, the course of the disease is not universal in that all or even a significant percentage of carriers develop the Syndrome when they meet certain criteria such as leaving the region. People from Hinamizawa or who go there who then leave the area can develop the Syndrome under stress as recognized in WWII. Ryūgū Rena similarly develops the Syndrome under the stress of her parent's divorce and financial situation after they move away. Her return helps suppress the symptoms. Hence the legends that Oyashiro-sama, the jealous and vengeful locative deity of the region, punishes those who attempt to leave the region while forbidding strangers from entering. People entering the region can and do develop the Syndrome under stress. Maebara Keiichi represents the obvious example. Over the course of the arcs it becomes clear that Takano, Irie, Jirō, and their various minions use a vaccine to prevent developing the Syndrome. However, it is strongly suggested that by the end Takano, herself, has developed the Syndrome despite vaccinations. Other than Keiichi, she is the only outsider to develop the Syndrome.
For those who were born in the region or who lived there, staying in the region seems to prevent or suppress development of the Syndrome. Takano's research suggests that the presence of a "Queen Carrier" is responsible; however, this is shown to be untrue in that in arcs where Rika dies earlier, villagers do not start developing the Syndrome. Further, Rena, Sonozaki Shion, Hōjō Satoko, and Hōjō Satoshi develop the Syndrome in Hinamizawa. Characters such as Akasaka Mamoru who spent time in Hinamizawa a few years before to investigate a kidnapping never develops it even though he suffers the stress of his wife dying in some arcs. For her part, Shion does not appear to develop her Syndrome when she was outside the region.
How one acquires the parasite is unknown. It cannot seem to exist outside of a living host. This would argue against an airborne pathogen or one that can exist for a brief time in food or on a surface. This would suggest passage by direct physical contact; however, such contact appears to be very minimal rather than intimate.
The pathogen appears to cause death through its extreme symptoms or significant to fatal brain damage as the victim progresses to L5 status. While paranoid and delusional, Keiichi dies because his formication leads him to claw out his own neck. Rena also claws at her throat and imagines "maggots" crawling under her skin as does, eventually, Takano herself. Irie prevents Satoshi from clawing his throat, but he still develops severe brain damage. "Severe brain damage" is irreversible; brain tissue does not regenerate. This would suggest that the "damage" is more functional rather than structural given that in the end Irie suggests Satoshi is showing very early signs of improvement. According to Irie, when Satoshi's sedation is withdrawn, he achieves consciousness but continues to suffer from severe delusions and hallucinations.
Progress of Research
The first treatment is created in 1980 during the period of Hōjō Satoko's hospitalization. Irie develops the medicine C-103 from Rika's blood. The treatment successfully reduces Satoko from L5 to a L3 status. However, she would have to continue to receive this medicine three times a day in injections, or else she would suffer a relapse. The exact nature of "C-103" is unexplained. If it is an actual "antibody," then it proves a rather poor agent for passive immunity. It appears, instead, to suppress the pathogen. The actual vaccine Takano, Irie, and others use appears to protect them, but then it ultimately fails Takano. One should not expect complete scientific rigor in fiction that involves multiple time fragments and a goddess.
During this same period of time Takano Miyo develops H-173, a drug designed to induce the L5 symptoms. Its main reason for its developed was for use in the military, since her initial backers decided that Japan would need a threatening biological weapon to compete with other large countries, especially nuclear powers. Takano uses this agent in 1983 to induce Tomitake Jirō to kill himself in all of the respective arcs in which he dies in order to protect her plan to instigate emergency manual #34.
Around 1982, Irie creates C-117. It is shown to be an effective treatment such that Satoko only has to take two shots per day. However it ultimately proves to be useless as a "vaccine" or preventative for those who already infected, such as Takano Miyo who progresses to L5 near the end of Matsuribayashi-hen, since she did visit Hinamizawa a few times before C-117's development.
In 1983, he creates C-120. This is the medicine that Rika tried to use on Shion in Meakashi-hen and offer to Rena in Tsumihoroboshi-hen: the Crazy Medicine. It supposedly has the power to reverse the effects of L5 down to around L2 or L3 with one injection. However, it shows an extremely negative effect on uninfected individuals such as Rika. Those who are injected with this medicine who are L1 or L2 suffer muscle spasms, itching at the lymph nodes, and extreme loss of stamina, since the medicine's purpose is to depress hormone levels.
In Miotsukushi-hen, Takano develops an advanced version of H-173 called H-173-02 which is capable of triggering the symptoms in large area through the air. She prepares as a last resort should all of her plans fail.
On the Emergency Manual #34
The Furudes were identified as the supposed "Queen Carriers" of the parasite, with the Queen being the latest born female. Hifumi Takano theorized that as soon as 48 hours after the Queen Carrier dies, the parasites will go out of control, causing everyone in the village to advance to L5 status. This is the reason for creating the emergency manual #34, which gives detailed plans for the termination of the entire village if such a case occurs. However, in Watanagashi-hen and Meakashi-hen, Furude Rika is dead for more than 48 hours with no effect. This means that the queen carrier theory is inaccurate or completely incorrect. However it is certain the Furude family contains an antibody or other substance that can suppress the syndrome.
On the Final Arc
The Irie Institution was always run secretly by Takano, who publicly appears as a nurse working under Irie. The Institute is scheduled to be disassembled around 1988. Irie planned to conduct research aimed at eradicating the disease in the remaining time while Takano, with Tokyo's backing, planned to innitiate the Great Hinamizawa Disaster to preserve her adoptive grandfather's research and, in her mind, become a "goddess" forever remembered. Unbeknownst to her, Nomura and Tokyo intended to use it to shift political power to their faction while disposing of Takano. When the main characters succeed in stopping Takano's plans, Nomura approves Takano's forced suicide to allow passage of the blame to her while achieving her and her group's political gains.
When Takano is eventually captured, Irie recognizes she suffers from Hinamizawa Syndrome given her continuous scratching at her throat. Irie is allowed to direct the above-ground clinic and resume his research on a cure, while a new director was chosen to direct the research. Takano, having been under the effects of L5, is to be treated and then handled by a disciplinary committee after becoming stable. The Irie Clinic is eventually sold to a private party and handled as a regular clinic afterwards.
Flaws in Dr. Takano's Report
In his report, Dr. Takano stated that Hinamizawa Syndrome was untreatable and irreversible. He also stated that anyone who enters the village shall be infected by Hinamizawa Syndrome no matter what, although the activation of the Syndrome will depend on the patient's mental condition. Despite this, a number of people, including tourists, are able to come and leave the village freely without showing symptoms afterwards.
In Tsumihoroboshi-hen, Keiichi successfully rescues Rena who was about to enter the end-stage of L5 in Hinamizawa Syndrome. It was revealed later that Rena was able to return from L5 back to L2 without the use of medication. Irie invented a proto-type of immunization shot which later became the base of the completed C-120 shot. C-120 shot was able to give immunization to anyone who enters the village and, to some extent, suppress symptoms in advanced stages of the disease. Again, Takano had received the C-120 shot yet eventually developed the Syndrome in the final arc.
Levels and rankings in Hinamizawa Syndrome
According to Dr. Takano's research in Matsuribayashi-hen, Hinamizawa Syndrome has five different stages, ranging from L1 (weakest) to L5 (strongest). A list of them is below.
Level One and Two
Weakest levels: almost all villagers and residents of Hinamizawa are infected and remain at either L1 or L2. The syndrome does not cause apparent changes until its later stages. This indicates that the entire village is highly unstable and will easily grow hostile from any stress or anxiety, such as the dam project. Some more than others, like Keiichi, are susceptible to simple paranoia and stress, which has been shown to activate the syndrome.
Beginning at L3, the mental condition of the patient will start to deteriorate and they become mentally and emotionally unstable. According to Irie in Minagoroshi-hen, Satoko was already in the end-stage of L3 before starting treatment.
Paranoia and hallucinations start to appear surrounding the onset of L4, as in the case of Keiichi in the later half of Onikakushi-hen.
Strongest level: this is when people began to hear 'Oyashiro-sama's footsteps,' and patients are known to start clawing at their own flesh. In some cases, there is a previous psychological motive that serves as a catalyst for the scratching. For example, Rena hallucinated that her wrist and neck were infested by maggots because of a previous incident regarding her belief that her blood from her mother consisted of maggots. This is an example of extreme formication. Formication is when a person suffers from the sensation that insects are crawling under their skin and scratches intensively to either remove the imaginary parasite or to simply end the pain. It is a real symptom to certain sexually-transmitted diseases such as syphilis and herpes. Skin diseases can cause this form of extreme irritation to the skin. Formication occurs in real life due to excessive use of amphetamines, suggesting the police station's wondering of whether Keiichi used narcotics as a provocative of his suicide in the first arc. There are several mistakes on the characters' views on the formication properties of the syndrome. Irie claimed that drugs did not result in "clawing at the throat," although formication does occur when under the influence of narcotics. It is revealed in Matsuribayashi-hen that C-117 is developed to be a trial-stage vaccine for anyone visiting Hinamizawa.