Tradition: Japanese Mythology
Alternative Names: 小玉鼠, Kodama Mouse, Kodama Rat
Category: Rat
The Myth
Kodama Nezumi is a supernatural creature known among the matagi, traditional hunters of Akita Prefecture, particularly in Kitaakita and Senboku districts. It resembles a swollen Japanese dormouse and is said to suddenly burst with a loud popping or explosive sound. Hearing this noise was considered an ominous sign that foretold failed hunts and other misfortunes. In some communities, the sound was believed to signal the displeasure of the mountain deity, and hunters who heard it were expected to return home rather than continue into the mountains.
Regional traditions describe the creature bursting along its back, and hunters recalled its sound as either louder than a gunshot or a soft, sudden pop. Some believed that reciting a protective Buddhist invocation three times could help ward off its influence, although speaking about the creature itself was also considered unlucky. The sound was associated with accidents and disasters, including a tale of a hunter whose sleeping shelter caught fire after he heard it.
Legends about the creature’s origin tell of a woman who sought shelter in a mountain hut during winter. One group of hunters refused her because women were forbidden in the mountains, while another took pity on her and offered her lodging. The woman, revealed to be the mountain deity, gave birth to twelve children on branches of the mizuki tree before flying away. The hunters who sheltered her were rewarded with good fortune, while those who rejected her were transformed into Kodama Nezumi. According to some versions, the transformed hunters resented their fate and caused misfortune by bursting with a loud noise.
Despite its supernatural reputation, Kodama Nezumi is identified in folklore research with the Japanese dormouse, a small mammal that hibernates curled into a ball. During winter logging, dormant dormice could tumble out of trees, and workers reportedly called them kinoko-tama. Folklorist Mutō Tetsujō suggested that the creature’s name and its echoing burst might be connected to kodama, the Japanese word for an echo or a tree spirit.
Sources
“Kodama Nezumi.” 新版TYZ 妖怪図鑑 (New TYZ Yokai Encyclopedia). https://tyz-yokai.blog.jp/archives/1010654298.html