According to some fans, the "Legend of the Tailed Beasts" is an epic story from Japanese mythology which Naruto author Masashi Kishimoto draws from to create the tailed beasts in his work. It appears, however, to be an example of internet-based fakelore which originated on the Chinese internet.
The veracity of the legend breaks when it is cross-referenced with non-fandom sources on Japanese folklore. For example, the isonade, which is held to be the three-tailed beast in this account, is in fact equipped with only one large, hook-covered tail, and the "houkou" (actually a Chinese creature called penghou), named as the five-tailed beast, has no tail at all.