Haimushi is one of the 63 creepy germs written in Harikikigaki, a book of medical knowledge written in 1568 by a unknown resident of Osaka. This tiny malevolent creature is believed to cause human illness during the 16th century in Japan.
It is a creature with appetite for rice and causes problems with the lungs. If the Haimushi exits the lungs and cannot find its way back, it turns into a fiery will-o'-wisp hitodama and the person dies.
The herb byakujutsu is effective in warding off Haimushi.