Tradition / Region: Japanese mythology
Alternative names: Koshin Mountain Wildcat, Koshinzan Yamaneko
Category: Cat
The Myth
The Koshin-yama Yamaneko was a gigantic wildcat that had lived for hundreds of years, growing to the size of a calf and gaining immense supernatural powers. Its face resembled that of a raging tiger, its mouth stretched to its ears and was redder than blood, its fangs were as white as swords, and although its body was human-like, it rode a grotesque horse formed from an ancient tree spirit. Its eyes shone like torches, and after revealing its true form, they gleamed like mirrors while its whiskers resembled snowy pampas grass. It could command the beasts of the mountain, ride tree spirits as horses, speak human language, and even had the mountain and land gods as its servants.
Seventeen years before the events of the story, the local samurai Akaiwa Ikkaku climbed Mount Koshin to prove his bravery. Unknown to everyone, he was killed and devoured by the monstrous wildcat. The creature stole his clothes, assumed his appearance, and descended from the mountain to live in his place. It sought to possess Ikkaku’s beautiful second wife, Madoi, whose life was eventually drained through sleeping with the disguised monster. The false Ikkaku then continued living among humans, abusing his eldest son Kakutaro while living with the wicked woman Funamushi, whose greedy nature allowed her to remain unaffected by the monster’s supernatural influence.
Years later, the Dog Warrior Inukai Genpachi arrived in the region while searching for his scattered companions. After hearing rumors of a monstrous wildcat living on Mount Koshin, he became lost in the mountain during the night. There he encountered the mysterious horseman whose blazing eyes pierced the darkness. Genpachi fired an arrow that struck the rider’s left eye, forcing the monster and its attendants to flee. Soon afterward, he met the ghost of the real Akaiwa Ikkaku, who revealed the truth about his murder and begged Genpachi to save his son Kakutaro from the impostor.
Genpachi descended the mountain and uncovered the schemes of the false Ikkaku and Funamushi. They falsely accused Kakutaro’s wife Hinaginu and eventually demanded that her unborn child be sacrificed to restore the monster’s wounded eye. Rather than allow others to suffer, Hinaginu stabbed herself in the stomach. At that moment the sacred Jewel of Propriety burst from her body and flew across the room, shattering the chest of the false Ikkaku with divine punishment.
As the battle continued, the false Ikkaku rose again, cast aside his human disguise, and revealed himself as the monstrous wildcat. Declaring that only by tearing apart his enemies, drinking their blood, and devouring their flesh could he preserve his supernatural power, he attacked Kakutaro and Genpachi. After a fierce struggle, Kakutaro severed the monster’s hip, brought it crashing to the ground, and finally pierced its throat, avenging the death of his true father.
Although the monster’s body was burned, strange illnesses and supernatural disasters continued to plague the region. Its ashes were eventually gathered and reburied beneath a cat mound, appeasing the wildcat’s lingering curse. Afterward, peace returned, and it was said that rats no longer came near the surrounding fields.
Sources
Takahashi, Toshihiro. “庚申山の山猫 (Mountain Cat of Mt. Kōshin).” 新版TYZ 妖怪図鑑 (New TYZ Yokai Encyclopedia). August 13, 2018. Accessed July 28, 2026. https://tyz-yokai.blog.jp/archives/1071974070.html