The Mishima Corporation "legitimately" control the richer people in Japan, a massive umbrella corporation that seized power after the war. Below them, the poor are controlled by the gangs, yakuza thugs and organised criminals. Both rule with an iron fist and a reign of terror. However, the people cannot survive without them. They both protect and serve the people, while making millions from extortion or "taxes".
You are a criminal underling in such a place, a member of the infamous Sumiyoshi-kai. Whatever your ambition is, whether it be to control the gangs or overthrow the government, is yours to take.