In this essay the author presents the principles of one important sector of social organization in Japan, and establish its framework. Japanese kinship structure, with its multiple historical and local factors, and unlike that of the Chinese or of the Hindus, does not belong to the category of unilineal systems, nor to any kind of descent pattern found in the published literature of social anthropology. Social anthropology, developed by micro-synchronic studies of simpler societies, and with its major analysis devoted to descent systems, has to face in Japan a critical methodological test. In this essay, the author, as a social anthropologist, want to overcome these drawbacks of anthropological method, and to demonstrate one of the new approaches by which an anthropologist can cope with the data from a sophisticated society