'Zennyo Ryūō (善女竜王 lit. 'Dragon Ruler Zennyo') is a dragon n Japanese mythology. Other spellings and variations of the name include Zennyo Ryuo, Zen-nyo-ryu-o, Zentatsu and Zen-tatsu.
A common description of Zennyo in the Shinsen'en stories is a small dragon (approximately two meters long) with a small gold snake on his head. It is also able to appear in human form. However, its dragon tail will remain visible.
Most stories agree that Zennyo's prefered home was in pond and lakes. He often received prayers and offerings to produce rainfall.
Zennyo was originally described as living in a pond at Mount Muro. A shrine was built to this dragon king some time after 781-783 AD. This shrine was used to give offerings to Zennyo in return for rain. Twin dragon models made of materiels like straw and reeds are one such offering. Other sources claimed that Zennyo was originally one of the dragon (or naga) kings of Anavatapta pond, the place in the Himalayas where many rivers start.
Zennyo at Shinsen'en
Shinsen'en (or Shinzen'en) had original been a garden used by the wealthy for entertainment. At times of drought, the water from the pond had been given to farmers so that they could irrigate their lands, meaning the pond already had a connection to water providing. Zennyo's move was attributed to the Buddist Shingon monks, who performed rituals which invoked the dragon's appearance. The monks became responsible for the rainmaking rituals required to persuade or coerce Zennyo into providing the rain. It was sightings from these monks that showed Zennyo to be a golden dragon with a snake on his head.
The Dragon Caves
There is another tale that describes Zennyo coming to Muro. It is said that a high-ranking lady fell into the pond at Sarusawa, Zennyo previous home, and drowned. Zennyo fled to another pond at Mount Kasuga, until a body was thrown into it. His final destination was Mount Muro, where he took residence in the local caves.
Some time later, a Buddist priest called Nittai wished to visit Zennyo. After travelling through the caves, Nittai found a palace with a sky above it. A part of the Buddish 'Lotus Sutra' was also here. Without appearing, Zennyo asked why he was there. Nittai replied that he wished to see the dragon king. Zennyo gave instructions of a place that Nittai must travel to.
Nittai left the caves and followed the instructions. As he arrived, Zennyo rose from the ground dressed in a robe and crown. A shrine was built on that spot by Nittai where requests for rain could be performed.
Keien and the Dragon Lady
Keien was a Buddist priest who lived as a hermit on Mount Muro, near the Dragon Caves. One day he encountered a well-dressed woman, who concealed her face. She asked to be taught the mundra of Buddha. He asked who she was, and received the reply that she was the dragon Zennyo. After teaching her the mundra, he asked to see her face. She told him that her face was too terrible to look at, but that she would fufil the request. Streching out her little finger, which was a dragon claw, a five coloured light came out. At this, Zennyo vanished.
- Fowler, Sherry (1997)