The Japanese word refers to the spirit of a kami or the soul of a dead person. It is composed of two characters, the first of which, , is a simply an honorific. The second, means "spirit". The character pair 神霊, also read mitama, is used exclusively to refer to a kami's spirit. Significantly, the term is a synonym of shintai, the object which in a Shinto shrine houses the enshrined kami. British Japanologist William George Aston (1841-1911) believed the mitama to be comparable as a concept to the Jewish Shekhinah.
Early Japanese definitions of the mitama, developed later by many thinkers like Motoori Norinaga, maintain it consists of several "souls", relatively independent one from the other. The most developed is the , a Shinto theory according to which the of both kami and human beings consists of one spirit and four souls. The four souls are the , the , the and the . According to the theory, each of the souls making up the spirit has a character and a function of its own; they all exist at the same time, complementing each other. In the Nihon Shoki, kami Ōnamuchi actually meets his kushi-mitama and shiki-mitama, but does not even recognize them. The four seem moreover to have a different importance, and different thinkers have described their interaction differently.