True to the meaning of its name, a ko-dama
is the spirit of a tree. Not all trees have ko-dama
dwelling in them, however, and usually these entitites tend to inhabit trees of very great age or size. It is said a person who cuts down a tree with a ko-dama
living in it will bring calamity upon their entire village, and often the sacred rope called shimenawa
is wound around trunks thought to contain these spirits in order to protect them.
While ko-dama are generally invisible to human eyes, they are thought to mischievously play with and mimic human voices, creating echos in the forest. "Echo" has also come to be another meaning of the word kodama.1
1. Mizuki vol. 1 2003, p. 51