What is the tesso?
The tesso is a yokai in the form of a large rat, or a vast swarm of rats, with teeth as hard as iron. It is said to be the grudge of the Heian-period monk Raigo transformed into rats, and is also called “Raigo’s rats.” Toriyama Sekien drew it in his Edo-period yokai books as a great rat tearing through scriptures.
The legend of Raigo’s grudge
Raigo was a high priest of Miidera (Onjoji) Temple in Omi Province. Asked by Emperor Shirakawa to pray for the birth of a prince, he succeeded, and as his reward asked for permission to build an ordination platform at Miidera. But the opposition of its rival, Enryakuji Temple on Mount Hiei, prevented his wish from being granted, and Raigo, enraged, fasted until he died. His grudge became 84,000 rats with iron teeth that swarmed over Mount Hiei and devoured its scriptures and Buddhist statues. The story is recorded in The Tale of the Heike and the Taiheiki.
The Rat Shrine
On Mount Hiei, a shrine was built to calm Raigo’s spirit and worship him as a god, and it came to be called the “Rat Shrine,” it is said. The tesso is a yokai born against the background of the fierce rivalries between temples.
