text: who reigns over japan? pllzzz japan has a prime minister; is the english political nomenclature of the head of government of japan, although the literal translation is prime minister of the cabinet.the prime minister is appointed by the emperor of japan after being designated by the diet from among its members, and must enjoy the confidence of the house of representatives to remain in office. the prime minister is the head of the cabinet and appoints and dismisses the ministers of state. the current prime minister of japan, since 2001, is junichiro koizumi.