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Nomura and Iwashi explaining the existence of Class-Cs in Higurashi no Naku Koro ni Kaku: Outbreak

The Class-C Brain Parasitic Virus (丙種脳寄生型ウイルス Heishu Nou Kisei-gata Uirusu) or "Class-Cs (丙種 Heishu)" for short, refer to symbiotic viruses present globally in the frontal lobes of 99% of the human population. It has also been hypothesized by the United Nations (UN) and Hifumi Takano to be the cause of all cultural and religious divisions, and differences in ideologies in the world. It is first brought up in Higurashi no Naku Koro ni Kaku: Outbreak, and later explored in more detail in the Outbreak and Kamikashimashi chapters of Higurashi no Naku Koro ni Hou.



The existence of Class-C Brain parasites is not public knowledge, since it was an informal study conducted by the United Nations in 1948; which resulted in some startling findings. Class-Cs were discovered by the UN decades before research into the Hinamizawa Syndrome began, by a German doctor of the Nazi regime. It was estimated that Class-Cs infect around 99% of the total human population on earth, and hypothesized that its existence may even date back to the origin of the human race.


It is said that hundreds of such virus strains exist and that coincidentally, the distribution map of various strains matched those of the national borders of the present times and also those of religious distribution maps. This led to an unsettling notion that cultural characteristics of different countries, races, and standards of social life were all a result of an indirect influence from Class-Cs. Based on this discovery, the main driving point of extreme measures such as genocides of specific races during that period were also suspected to be one such influence by the viruses.

Measures taken by the UN and other countries

The surprising discoveries regarding Class-C viruses led to the formation of a secret investigative committee by the UN. As a result, the possibility that Class-Cs indirectly led to crimes and other unspeakable acts committed by humans was brought forth. The UN became alarmed and pushed for the eradication of such viruses, but the committee opined that ethnic cleansing propaganda; such as those of the Nazis; may be aggravated. The information was hence deemed too dangerous. After this, research on Class-Cs was prohibited by the UN in 1995, and the findings were destroyed. Even so, each country delved into their own secret investigations into the virus. There are no proper research exchanges, so the level of investigation that each country is at remains unclear. In the late 1960s, a group of medical institutions in Japan formed a study community to research the virus in secret, which was the basis of the findings put forth by the Alphabet Council in the present day.

Class-Cs were later brought forward by the Head of the Alphabet Council to the Japanese government on the 6th of July, 1983 in order to push forward their request to quarantine Hinamizawa and its surrounding areas in Kaku and Outbreak to prevent a predicted outbreak, which could be followed by riots and genocides.


Symbiosis and Influence on Host

Class-Cs have a high affinity to the human brain. Hence, their existence wasn't confirmed until the modern times, due to the viruses seemingly being asymptomatic. They are mostly harmless and co-exist with human hosts in a symbiotic manner. However, it turns out that Class-Cs can influence the human brain to an extent and are hence friendly to hosts infected with the same parasite, and hostile towards those infected by others. Therefore, it was theorized that they may be the inherent reason for the divisions in the human race, with regard to nationalities and religions, amongst other ideologies.

In fact, further hypotheses suggested that the influence of Class-Cs may run deeper; to the extent of influencing fundamental characteristics of human beings such as their personalities and behaviors. This explained the cause of several race-specific tendencies.


Not all strains of Class-C are the same, and there seem to be some which result in a lower quality of living or are dangerous for the infected. Some such viruses have the potential to turn pathogenic.

The virus responsible for the Hinamizawa Syndrome is only one such strain of many such parasitic pathogens present throughout the world, but possesses extremely unique characteristics in comparison to other types. The parasite causing the syndrome is naturally symbiotic as long as the host is not under a considerable amount of psychological stress or leaves Hinamizawa for a period of time. This ensures a favorable environment for the parasite. But in rare cases where the host environment turns hostile, the virus turns pathogenic and the host loses their sense of reason and develop psychosis and antisocial tendencies. Eventually, the terminal stage will result in permanent brain damage or end with the host's death after they give in to an escalating sensation of itchiness and die from hemorrhagic shock after scratching out their own throat.

Towards the end of Kamikashimashi, the alien Une Virus which had arrived on earth shortly before the outbreak of the Hinamizawa Syndrome is exposed as one such terrifying Class-C pathogen. It turns out to be a highly contagious killer virus which latches onto host after host until they've depleted them of all nourishment, leaving them for dead. The Une virus soon turns into a pandemic and after seven weeks of infection, the human population decreases by a whopping 20 percent.


Hanyuu or Oyashiro-sama, the "leader" of the pathogens whom she refers to a her "tribe", is the spiritual entity who watches over Hinamizawa; trying to ensure that the pathogen endemic to the land does not run amok. She calls those who succumb to the Hinamizawa Syndrome her "brethren", hinting that the parasite could be considered as the physical manifestation of a godly entity.

In Kamikashimashi, the existence of two more such spiritual entities are introduced, being Tamurahime no Mikoto and Une. Thus, the conflict ensuing amongst these entities appeared to manifest as diseases in the hosts they infect. The leader of the godly entity may possess a human miko as a medium of contact with humans. The miko are also entrusted to carry out the will of the gods they serve. Rika Furude is one such example. Apparently, a miko may also be elected by an entity as well such as in the case of Takano, in Outbreak and Kamikashimashi.


Class-Cs are shown to be biologically competitive, which causes a dispute amongst the spiritual entities that lead them. Hanyuu explains that Class-C parasites can only take a host on a first come, first served basis if two or more viruses were of equal strength. The Une Virus and the strain of η-173, the synthetic virus that had been developed to cause an outbreak of the Hinamizawa Syndrome, were an example of such strains which were of equal strength; whereas the strain managed by Tamura was far weaker than the both of them.