According to the japanese folklore, when a cockfighting rooster and its owner are murdered, their spirits can fuse together into a monstrous chicken-human hybrid called an onnen no niwatori. This ghost looks like a man-sized bipedal chicken with grey, plucked skin, pincers for hands, and a large red comb on top of its head.

Onnen no niwatori are so frightful to behold that people who see them suffer paralysis which can last for several days. After the limb paralysis wears off, it takes much longer to fully regain the ability to speak.

Onnen no niwatori comes from Chikuzen bakemono emaki, an Edo period yokai picture scroll that depicts 40 yōkai paintings and stories not found anywhere else.

Cockfighting was strictly prohibited in Japan in 1815, but people still held them in remote areas and mountains, away from the public eye. One such place was at Ryū-ga-fuchi on the Tengu River in Bungo Province. There, at the foot of a tall mountain, was a cave dedicated to a water god, and it was only visited once a year, by a few priests and worshipers making offerings to the water god.

One day, about thirty people gathered there for cockfighting. A man from Buzen Province called Takatsuru was the victor, and took the prize money of 635 ryō. The losers conspired against him, and they attacked Takatsuru and his four companions. They tied them up and weighted them down with stones, and then tossed them into the deep waters of Ryū-ga-fuchi and drowned them. They also captured Takatsuru’s prize chicken and were going to eat it, but some of the conspirators suggested that eating Takatsuru’s chicken was a step too far; Takatsuru’s spirit might give them indigestion. Instead, they suggested sending the chicken to be Takatsuru’s companion in the underworld. They ripped out its feathers and tossed it into the river with Takatsuru, saying “Go and cockfight in hell!”

Immediately afterwords, a monster emerged from the water, formed of the fused spirits of Takatsuru and his chicken. Everyone there lost all the strength in their limbs and was paralyzed with fear. Most of the men never recovered, and starved to death where they collapsed. However, four of the assailants suffered only lightly from Takatsuru’s curse and somehow managed to recover after about five days, but their mouths stiffened up and they lost the ability to speak clearly.

Eventually the four survivors recovered their ability to speak, and they were arrested and interrogated. The 635 ryō was never recovered.