A Broken Promise: The Monk Raigo and the Legend of the Iron Rat

The tesso's story doesn't begin with a giant rat. It begins with a promise that was never kept. A monk was asked to pray for something, and his prayer was answered, yet the reward he had been promised never arrived. His bitterness took the form of a rat and went after the very thing a temple treasures most: its sutras, the sacred Buddhist texts. Let's take a gentle walk through the story of Raigo, the monk behind the tesso, together with the relationship between the two temples in the background.

The prayer that worked

Raigo is said to have been a monk of Mii-dera, in Omi Province, today's Shiga Prefecture. Mii-dera's formal name is Onjo-ji. It's an old temple in Otsu, on the shore of Lake Biwa, Japan's largest lake.

According to the legend, an emperor longed for the birth of a prince and entrusted the prayer to Raigo. He promised, it's said, that if a prince were born, Raigo could ask for any reward he liked. Raigo's prayer was answered, and a prince was born safe and well.

What Raigo asked for was a kaidan, an ordination platform, for Mii-dera. A kaidan is where new monks formally receive the Buddhist precepts. With one, Mii-dera could ordain its own monks. For the temple, it was an enormously important wish. But the promise was never kept.

Two Tendai temples, side by side

Why not? The story goes that Enryaku-ji, the great temple on Mount Hiei, fiercely opposed it.

Mii-dera and Enryaku-ji both belong to the Tendai school of Buddhism. They come from the same roots, but in time the Enryaku-ji side came to be called the Sanmon, the "Mountain Gate," and the Mii-dera side the Jimon, the "Temple Gate," and the two were rivals for a very long time. To have an ordination platform was to have the power to raise new monks. For Enryaku-ji, a kaidan at Mii-dera was not something to let pass.

Mount Hiei overlooking Lake Biwa, and Otsu at its foot: on a map, the two temples are close neighbors. Their rivalry is the ground the tesso legend grew from.

A grudge becomes a rat

Raigo, betrayed, is said to have refused all food in his bitterness until he died. And the prince born of his prayers, the story goes, died while still a small child.

It doesn't end there. In tales told later, Raigo's grudge became a giant rat with teeth as hard as iron. Leading a horde of rats, it swarmed up Mount Hiei and gnawed through sutras and Buddhist statues. There is also a story that Enryaku-ji, at its wits' end, enshrined Raigo's spirit as a god to calm it.

Raigo's story appears in war chronicles such as The Tale of the Heike and the Taiheiki. A quarrel between two powerful temples was handed down for centuries in the shape of a rat, a familiar and troublesome little creature. For temples whose greatest treasures were written on paper, it's hard to think of a more frightening form of revenge than a rat that chews paper.

The name "tesso"

Taking its name from the monk, this rat has also been called "Raigo's rat." In the Edo period, the painter Toriyama Sekien, famous for his yokai pictures, drew it under the name "tesso," the iron rat. You can read more about Sekien in our article on Toriyama Sekien.

On the tesso's Yokaipedia page here at Pixel Yokai, an iron-gray rat holds a half-chewed sutra scroll tight. On the Yokai Map, you'll find it at Mii-dera in Shiga.

A yokai that teaches, in a slightly scary way, why promises matter. In an old temple on the shore of Lake Biwa, that long story is still sleeping.