Kidomaru is an oni (or ogre, a creature from Japanese folklore) that appears in Kamakura period texts such as the collection of stories entitled "Kokon Chomonshu" (A collection of Tales Heard, Past and Present).
"Kokon Chomonshu" states the following. When the military commander MINAMOTO no Yorimitsu known for the subjugation of Shuten Doji went to the home of his younger brother, MINAMOTO no Yorinobu, Kidomaru was caught in the toilet. Yorimitsu told Yorinobu to put it into chains tightly for sure and spent the night at Yorinobu's residence. Kidomaru escaped from the chain with ease, cursed Yorimitsu and spied on him in his bed.
Yorimitsu became aware of this and told his attendants that 'Tomorrow I will go to pray at Kurama.'
Kidomaru then went on ahead to Kurama and killed a free-range ox at Ichiharano and hid inside the body where he awaited Yorimitsu. However, Yorimitsu discovered Kidomaru's plan and he ordered WATANABE no Tsuna to shoot an arrow into the ox. Kidomaru emerged from the ox's carcass and attempted to attack Yorimitsu but it is said that Yorimitsu cut him down with a single blow. Sekien TORIYAMA's book of images of ghosts and demons, "Konjaku Hyakki Shui" (Supplement to The Hundred Demons from the Present and the Past), refers to Kidomaru as 'Kido' and depicts him in the snow wearing an ox hide awaiting Yorimitsu at Ichiharano.
This "Kokon Chomonshu" story of Kidomaru is well known but other tales appear in musha-e (prints depicting battle scenes and heroic armored warriors.) books and legends. The following legend about Kidomaru being the child of Shuten Doji is told in the folklore of Kumohara, Fukuchiyama City, Kyoto Prefecture. After MINAMOTO no Yorimitsu killed Shuten Doji, the young women who had been held captive by Shuten Doji were returned home but one of them developed a mental abnormality, becoming unable to return to her home and later giving birth to Shuten Doji's child in Kumohara. This baby grew teeth while being born and at around the ages of seven and eight he would kill deer and wild boar by throwing stones to eat them. This child eventually grew up to become Kidomaru and it is said that he targeted Yorimitsu in revenge for his father.
Similar to other stories claiming that Kidomaru was a child abandoned by Shuten Doji, other accounts of Kidomaru according to texts such as the military tale "Zen Taiheiki" state that he was originally a chigo (a boy kept by a pederast) on Mt. Hiei but that his wrongdoings caused him to be expelled from the mountain after which he dwelled in a cave in the mountains and became a thief.
According to Bakin KYOKUTEI's "Shitenno Shoto Iroku" (picaresque novel of the life of Yasusuke HAKAMADARE, a robber), Kidomaru met the thief Hakamadare described in "Konjaku Monogatarishu" (Anthology of Tales from the Past) at his mountain cave and competed in a magic competition. Images depicting this scene include the ukiyo-e "Kidomaru" by Kuniyoshi UTAGAWA and "Hakamadare Yasusuke Kidomaru Jutsukurabe no Zu" (battle picture of Yasusuke HAKAMADARE and Kidomaru) by Yoshitoshi TSUKIOKA.