The hack and slash action takes place in a state called Gishuamari during the Sengoku period. By slaying the late ruling family, the Sakurai clan, a man named Fujimori became the state's Daimyo.
As a ruler, he keeps an iron fist on the country and the way with which he took the Daimyo's throne made him enemies amongst the peasants and old noble families.
The player is a stray Samurai with the freedom to join any party, e.g. Fujimori's, the old noble houses' or the peasants.
Of course, with the freedom provided in the game, there are more than one route you can develop your story, betray your old employers and go under a new one, remove yourself from corruptive forces and join the battle for justice etc, just remember that the fate of the state rests within your hands.