Jubokko

Jubokko (樹木子 "Infant Tree ") is a tree-shaped yōkai in the folklore of Japan.

It is mentioned in several books relating to the subject of yōkai, including works by Shigeru Mizuki.

Jubokko Myth

According to folklore, the jubokko appears in places that were battlefields that left a particularly high death toll.

Its appearance does not differ much from an ordinary tree, but it becomes a yōkai tree after absorbing large amounts of human blood from those killed in battle, whereby the jubokko subsequently survives by feeding on it.

Also according to folklore, if a person passes near a jubokko, it would trap him and its branches would change shape to simulate tubes, through which it would absorb the victim's blood.

A jubokko that has fed on a person in this form would retain a fresh appearance.

Other mythical details include that when a jubokko is cut, it would drip blood, and that a judokko branch can help heal or decontaminate a person. 

Jubokko's Origin

Scholars of Japanese folklore such as Kunio Yanagita and Iwao Hino concluded in written works that there was no record of any yōkai that could have served as the origin for the jubokko idea.

A group of experts known as the To と学会 Academic Conference (to gakkai ) and headed by scholars Natsuhiko Kyogoku and Tada Natsumi, as well as writers Murakami Kenji and Yamamoto Hiroshi, concluded that, since no possible source exists or is known for the myth of this yōkai, or from which the myth could have evolved into its current form;

it can be speculated that the jubokko is indeed a fictional creature entirely created by Shigeru Mizuki.

For his part, at one point Mizuki went so far as to state that about 30 yōkais depicted in his manga GeGeGe no Kitaro and other of his works had been invented by him, but he did not specify which of the creatures were his authorship and which were not.