Gagoze

It can also be found in the text of the Heian period Nihon Ryōiki (in the story, 雷の憙を得て生ま令めし子の強き力在る縁," On a Boy of Great Strength Who Was Born of the Thunder’s Rejoicing"), the Honchō Monzui, among others.

[1] In classical yōkai drawings such as the Gazu Hyakki Yagyō by Toriyama Sekien, it is depicted as an oni with the appearance of a monk.

[1][2][3][4] Tetsuo Yamaori, in a thesis on the true nature of the concepts in old Japanese gods (kami), took note of the worldview in the background of this story.

Observing that the first half involved lightning turning into a "small child" and then immediately ascending back to the sky, and that the latter half had a "demonic spirit" that would only appear at night and whose true form cannot be checked without getting close to a light, Yamaori notes that this is a clear show of how spiritual beings originally had a very self-concealing nature.

However, the folklorist Kunio Yanagita denies this supposition and instead posits that this comes from how monsters would say "kamou zo" (咬もうぞ, I'll bite ya) as they appear.