I love yokai stories that reference other yokai stories. There are a lot of recurring characters, especially heroes, among yokai tales; especially among tales from the Kamakura period, when the legends of brave samurai from the previous era were popular. The rise of the military caste during this period is probably responsible for the popularity of amazing warrior stories from that time.
Cross-referencing other yokai seems to give a little bit of credence or believability to folk tales. We see Toriyama Sekien do this a lot when he makes up new tales. Some of the really famous yokai, such as Tamamo no Mae and Shukaku trace their roots all the way back to India and China, linking their Japanese versions to famous folk tales from those countries, and adding more depth to their biographies.
In a way, it’s almost like a folkloric “expanded universe” or fandom, where sometimes contradictory stories exist, but they still feel correct despite the irregularities.
Kidōmaru is the name of an oni who appears in Kokon chomonjū (“A Collection of Notable Tales Old and New”), a Kamakura period complication of myths and legends of the Heian period. Kidōmaru is his name, so I haven’t listed a translation, but the characters used roughly translate to “Oni Boy.” It sounds like a nickname, almost like “Billy the Kid.” I’m sure you could translation it a number of fun ways: “Li’l Oni” “Oni the Kid” or anything along those lines, but I will just call him Kidōmaru.
When speaking of oni, it is impossible to fail to mention Shuten Dōji, the king of the oni. We’ve also covered his right-hand man (woman?) on this blog: Ibaraki Dōji. Kidōmaru is another member of Shuten Dōji’s clan, and is sometimes said to be Shuten Dōji’s son!
His story takes place after the legendary samurai Minamoto no Yorimitsu (aka Raikō) and his party of heroes had subjugated Shuten Dōji and freed all of the women captured by the oni’s clan. The women were grateful to the samurai for rescuing them, and returned home to their villages. One of the women, however, didn’t return to her home. Instead, she traveled to the village of Kumohara, where she gave birth to a baby oni—Shuten Dōji’s son!
The boy was named Kidōmaru. He was born with a full set of teeth, and an oni’s strength. When he was only 7 or 8 years old, he was strong enough to kill a deer or a boar by throwing a single rock. By the time he had grown to an adult, he decided to get revenge on those who had slain his father.
Some versions of his story say that he was apprenticed as a temple servant to Mt. Hiei, just like his father was. And just like his father, he was eventually expelled from the temple for being a wicked, wretched little boy. He fled into the mountains and lived in a cave. He turned to robbing people to survive, and studied magic and honed his powers in his cave hideout.
Time passed, and the next thing we hear about Kidōmaru occurs when Raikō was visiting his younger brother, Minamoto no Yorinobu. Yoribonu had captured Kidōmaru in his bathroom—the story doesn’t say how or why this happened, but somehow, Yorinobu had locked the oni in the bathroom.
Raikō scolded his little brother for being so careless and not properly tying Kidōmaru up in ropes and chains. He then tied up the oni in chains to make sure he couldn’t escape and to show his brother how it was done. Raikō spent the night there just to make sure everything was OK.
During the night, Kidōmaru easily broke the chains that were holding him with his supernatural strength. He wanted to get his revenge on the cocky Raikō. He snuck up to Raikō’s door and spied on him. Raikō, however, noticed Kidōmaru spying on him. In a loud voice, he told his attendants that tomorrow morning they would ride to Kurama to make a pilgrimage to the temple there.
Hearing this Kidōmaru went ahead to set a trap for Raikō. He set up an ambush on the road near Ichiharano. He slaughtered a cow in one of the fields and climbed inside of its body to hide and wait for Raikō.
When Raikō and his companions arrived at Ichiharano, they easily saw through the oni’s disguise. Raikō’s best archer, Watanabe no Tsuna (the same Watanabe no Tsuna who cut off Ibaraki Dōji’s hand) shot an arrow through the cow’s body, injuring Kidōmaru.
Kidōmaru emerged from the cow’s corpse and charged at Raikō with all of his might. However, Raikō was too fast for him. He cut Kidōmaru down with a single stroke of his blade.