The Hinamizawa Syndrome (雛見沢症候群, Hinamizawa Shōkōgun) is a fictional organic brain disease of uncertain etiology, endemic to the residents of Hinamizawa. It appears to be 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 when the infected leaves the region or when the infected undergoes significant physiological or psychological stress. 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, a real-life 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 and die from the resulting blood loss.
Diseases and their research as they are portrayed in Higurashi no Naku Koro ni do not necessarily match real world scientific process or consensus. As Higurashi no Naku Koro ni is explicitly a work of supernatural fiction, total scientific accuracy is not to be expected.
Dr. Takano's Report on The Hinamizawa Syndrome
According to Matsuribayashi-hen, Dr. Takano Hifumi had already discovered the existence of the Hinamizawa Syndrome about 20 years prior to the story. He wrote a report regarding the town and the disease plaguing its residents, where its name was coined. His goal was to secure funds for its research, eventual treatment, and to increase awareness among the general public. However, Dr. Takano encounters political opposition and his research is ridiculed by authorities. This scars Dr. Takano emotionally and marks the beginning of his descent into senility.
After Dr. Takano's death, his adopted granddaughter Takano Miyo takes over the research on Hinamizawa Syndrome. She receives support and funds initially from Koizumi, a former superior of Dr. Takano, who felt guilty over betraying him and helping to suppress his research. Koizumi reveals to Takano Miyo that one of the soldiers from the Japanese garrison in Manchuria came from Hinamizawa and most likely suffered from the disease. He may have opened fire on the Chinese soldiers, 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 the existence of the Hinamizawa Syndrome since doing so would require Japan to accept the blame for the Incident, and China may use this information as political and moral leverage against Japan. Furthermore, this would require the Japanese government to essentially accept Japanese blame for the start of a war that ultimately led to the WWII. Therefore, its existence was covered-up and Dr. Takano's research was denied.
Further research in the Irie Institute
Takano Miyo restarts her grandfather's research with Koizumi's support from an organisation called "Tōkyō" who sponsored the Alphabet Project. While appearing as a village clinic, the Irie Clinic is actually an institute complete with secret underground facilities devoted to research into the Hinamizawa Syndrome, headed by Tokyo-sponsored researcher Irie Kyōsuke. The research that takes place is based on 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 confirm the presence of a pathogen that disappears from its host as soon as the host dies. The exact nature of the "parasite" and its origins is never fully revealed until Outbreak. The mystery surrounding the illness is the source of stories and legends concerning Furude Hanyū, named Oyashiro-sama by the villagers.
There are a few solid facts about the illness. It is known that most who contract Hinamizawa Syndrome will not exhibit symptoms, even after leaving the village. However, people from Hinamizawa or who go there who then leave the area can develop the Syndrome under stress, as recognized in WWII. In a contemporary example, Ryūgū Rena develops the Syndrome under the stress of her parent's divorce after several years living outside of Hinamizawa. Those who develop symptoms may experience relief upon returning to Hinamizawa. These symptoms were interpreted as the Curse of Oyashiro-sama, whose doctrine declared that villagers may not leave the village (to prevent the appearance of symptoms) and that outsiders may not enter (to prevent new infections). Those who do enter the region may become infected and develop the Syndrome under stress. Maebara Keiichi enters L5 stage after only a few months living in Hinamizawa in Onikakushi-hen. Takano Miyo, Irie Kyōsuke, Tomitake 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. She and Keiichi are the only outsiders known to naturally develop the Syndrome.
Takano's research suggests that the presence of a "Queen Carrier" is responsible for the repression of symptoms within Hinamizawa, identified as Furude Rika. However, this is shown to be untrue in that in arcs where Rika is killed by Sonozaki Shion, as villagers do not start developing the Syndrome. Further, Rena, Shion, Hōjō Satoko, and Hōjō Satoshi develop the Syndrome in Hinamizawa. It is unclear whether every person who spends time in Hinamizawa contracts the disease. Akasaka Mamoru spent several days living in Hinamizawa, but never develops symptoms even after undergoing severe stress outside of the village. This is not conclusive proof that he is not infected. Despite enduring stressful conditions outside of her home village, confirmed case Sonozaki Shion only develops symptoms in certain arcs where she returns to Hinamizawa, and it is implied many others have left the village without ever developing symptoms.
How one acquires the parasite is unknown, and there are contradictory statements regarding its spread. It is suggested that the pathogen is airborne; however, as it is also stated the pathogen can only exist within the body, this would seem impossible. Other referenced means of spread include contact with an infected person's bodily fluid.
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 effectiveness appears to be inconsistent in a way real life vaccines are not. Though Takano Miyo, Irie Kyōsuke, and Tomitake Jirō are protected through the vaccine for a time, Takano eventually shows symptoms of the syndrome.
Alongside C-103, Takano Miyo develops H-173, a drug designed to induce the L5 symptoms. This drug was created with the sponsorship of Tōkyō for use as a weapon by the Japanese Military. Though Tōkyō eventually ordered the distruction of H-173 under new leadership, some of the weapon is preserved. Takano uses this agent in 1983 to induce L5 symptoms in Tomitake Jirō, causing his death.
Around 1982, Irie creates C-117. The agent proves more effective in managing symptoms than C-103, and prevents Satoko from progressing beyond the L3 stage with only two shots.
In 1983, he creates C-120, also known as the Unknown Medicine. It supposedly has the power to reverse the effects of L5 down to around L2 or L3 with one injection by reducing the levels of certain hormones. Due to the function of the vaccine, those who are not at the L5 level may develop L5 symptoms if injected, as happens to Furude Rika when she attempts to treat Sonozaki Shion by force in Meakashi-hen.
In Miotsukushi-hen, Takano develops an advanced version of H-173 called H-173-02 which is capable of triggering the symptoms across a large area through the air. She prepares as a last resort should all of her plans fail.
In Kamikashimashi-hen, it is revealed that Takano had developed η-173, a strain of potent microorganisms which are capable of spreading the Hinamizawa Syndrome over a large area through the air. Most likely a variant of the original pathogen cultivated by Takano, η-173 is portable and capable of infecting those who are exposed to it, making it possible to spread the Hinamizawa Syndrome to areas outside of Hinamizawa. She unleashes this virus on the inhabitants of Hinamizawa and the surrounding localities upon the orders of Tamurahime no Mikoto in order to prevent the spread of the Une virus. This triggers the events of Outbreak.
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. Takano Hifumi theorized that upon the Queen Carrier's death, individuals infected will advance to L5 status between 24 and 48 hours. Thus Emergency Manual #34, which gives detailed plans for the termination of the entire village if such a case occurs, was created. However, in Watanagashi-hen and Meakashi-hen, Furude Rika is dead for more than 48 hours with no effect, so it can be assumed that the Queen Carrier theory is at least partially incorrect. However, it is certain the Furude family host an antibody or other substance that can alleviate the terminal symptoms of the syndrome.
On the Final Arc
The Irie Institute was scheduled to be disassembled around 1988. Irie Kyōsuke, its namesake and public head, planned to conduct research aimed at eradicating the disease in the remaining time. The true power within the institute lied with Takano Miyo, a woman publicly appearing as a nurse under Irie while backed by the far-right political group "Tōkyō". With the death of Takano's benefactor Koizumi, Takano's supporters suddenly turn on her. They ridicule the research they previously praised and order the infection to be eradicated and all evidence of the research destroyed. Faced with the end of her research, and with the support of a mysterious new benefactor from Tōkyō named Nomura, Takano creates a plan to initiate the execution of instructions left in Emergency Manual 34. Supposedly, a wide and sudden outbreak of Hinamizawa Syndrome symptoms would justify her grandfather's theories and and allow Takano to position herself as a god. Unbeknownst to Takano, Nomura intended to use it to shift political power to her faction while disposing of Takano.
When Takano is eventually captured, she is identified as having progressed to the L5 stage by Irie. 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. When the main characters succeeded in stopping Takano's plans to cause the Great Hinamizawa Disaster, Nomura approved Takano's death so that Takano may be made a scapegoat for Nomura's faction.
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 second 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, a condition in which a person suffers from the sensation that insects are crawling under their skin. This may lead to delusional parisitosis (which Rena is diagnosed with), and in turn self mutilation, in which a person cuts or scratches intensively to remove the imaginary parasite or to simply end the pain. There are a number of real life conditions known to induce formication. Several drugs (including some legal ones, such as SSRIs) can induce formication, influencing speculation that Keiichi had been under the influence of narcotics during Onikakushi-hen. 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.
- In Batsukoishi-hen, Keiichi becomes a victim of the apparent True Hinamizawa Syndrome, which turns people into mindless perverts. Again Takano wants to spread this virus and rule the world with men bowing down before her.
- The sensation of "maggots crawling under skin" can be described as a form of "tactile hallucination", similar to "cocaine bugs" in cocaine abusers, who at times experience prickling feeling of bugs under their skin.