No practical power - emperor's duties are ceremonial. Prime minister and the cabinet are the executive branch of government, diet's the legislative. Diet selects the prime minister, who's appointed to office by the emperor. Prime minister chooses his cabinet. Members of the diet are elected by the populace. Also a supreme Court for the judicial branch, independent from the legislative and executive. Smaller local segments of the government to handle matters for different prefectures, cities, and so on.

[Did.....did you get all that?]