Ever since Demon Slayer completed its run, fans have been quick to break down certain aspects of the series and analyze it. Fans have come up with some theories and the explanation provided for those claims are pretty convincing, to say the least.
It is not uncommon for anime series to take inspiration from a variety of sources. Demon Slayer, too, seems to have taken inspiration from other sources, as fans believe that the demons from the 12 Kizuki were modeled after diseases.
Disclaimer: This article contains spoilers and is based on the author's opinions.
Demon Slayer: Possibility of demons being modeled after diseases
Since Muzan killed most of the Lower Moon demons after Rui's death, fans haven't really had a chance to understand their combat abilities, which would further give them an understanding of the disease they were modeled after.
It's highly likely that the Lower Moon demons were modeled after diseases as well. However, this is speculative since the article is merely exploring theories put forth by the fanbase.
Daki’s human name was Ume, which means Plum, in Japanese. Her mother was suffering from a disease, and they lived in the Yoshiwara district.
The Kanji for syphilis is a combination of the Kanji characters Plum and poison. Considering that her mother lived in the Yoshiwara District, it is possible that she contracted syphilis.
Gyutaro could be a victim of Congenital Syphilis, which means his mother passed on the infection while he was in her womb.
Kaigaku from Demon Slayer could be modeled after Human Scabies, which is caused by an itch mite. His Blood Demon Art makes it look like his skin is cracking. Further, when his attacks land on Zenitsu, his skin cracks as well, which happens to be one of the main symptoms of this disease.
Fans believe that Gyokko was modeled after Amoebic Dysentery. This is a disease that is spread through water or by eating a fish infected by this parasite. When the infection worsens, a pot-like tumor grows on the body of the host.
It seems that Hantengu was modeled after Leprosy. The Upper Moon 4 has a huge bulge on his forehead and the disease is usually spread through insects.
Another fact that could serve as evidence is the fact that the bacteria causing the disease is called the “Lie Bacteria” in Japanese. Hantengu often lied to people in order to steal from them.
Nakime from Demon Slayer could be modeled after Infectious Conjunctivitis. The Kanji characters of her name can be translate to “for weeping eyes” and the fact that she has a pink colored eye (Infectious Conjunctivitis is also called Pink Eye) only makes the claim all the more believable.
Doma seems to be modeled after Stage 2 Tuberculosis, since his Blood Demon Art damages the lung tissue if the ice particles are inhaled by the demon hunters.
Kokushibyo was modeled after the Plague, or Black Death. The Upper Moon 1 wears a purple Kimono, which could be a reference to the purple patches that one receives after being infected.
The Japanese name for the Bubonic Plague is Kokushibyo, which is pretty close to the Upper Moon 1’s name.
The reason why demons might be modeled after diseases could be due to the fact that the first ever demon that came into existence was due to a disease. Its treatment remained incomplete, which is possibly why all succeeding demons are modeled after diseases as well.