Kodoku
Mythology & Folklore

for further reading: Atlas Obscura

Kodoku is often associated with onmyodo and its earlier predecessor, "Gu magic" from China. Kodoku are created by placing a number of poisonous insects into a jar and allowing them to kill one another. The surviving creature is said to become extremely powerful from being infused with the poison of the other creatures. This could then be used to create powerful curses.

The connection between onmyodo magic with its focus on the five elements of fire, water, earth, wood and metal can be seen in kodoku/gu magic's use of "five poisonous creatures" (centipede, scorpion, spider, toad and viper) that was recommended to be performed on the fifth day of the fifth lunar month (the day of the Dragon Boat Festival).

Relevance to MAO

Mao uses a kodoku in the form of a jar where he places poisonous insects. The poison that is created in the jar is used to treat his wounds (because of his association with Byoki). Byoki was made via this process as well. In Inuyasha Onigumo became Naraku via a kodoku process.