Tradition: Japanese Mythology
Alternative Names: 鉄鼠, Iron Rat, Raigō Nezumi
Category: Rat
The Myth
Tesso, meaning “Iron Rat,” is a monstrous supernatural rat born from the vengeful spirit of the Buddhist monk Raigō. During the reign of Emperor Shirakawa, Raigō served as abbot of Mii-dera in Shiga Prefecture. After praying for the birth of a royal heir, he was promised permission to build a new ordination hall at his monastery. However, the powerful rival temple Enryaku-ji pressured the Emperor into breaking his promise. In despair and anger, Raigō undertook a hunger strike and died after one hundred days.
Consumed by resentment, Raigō became an onryō, a vengeful ghost. His spirit was said to have appeared near the young Prince Taruhito, who died soon afterward, leaving the Emperor without an heir. Raigō’s spirit then transformed into a gigantic rat with a body as hard as stone and teeth and claws as strong as iron.
Tesso summoned a vast army of rats and led them against Enryaku-ji on Mount Hiei. The creatures gnawed through the monastery’s buildings, destroyed its furnishings, and devoured sacred Buddhist texts, scrolls, and even statues of the Buddha. The devastation continued until a shrine was established to appease Raigō’s spirit. According to tradition, Raigō’s shrine faces north toward Mount Hiei and Enryaku-ji, the monastery at the centre of his legendary vengeance.
Sources
“Tesso.” Yokai.com. https://yokai.com/tesso/