The title of the movie in Japanese is Sengoku Yaro. "Sengoku" means warring states and refers to the period in Japanese history when many warlords fought against each other in order to dominate more territory. This period is said to have lasted from 1467 to 1603. The "Yaro" part can be translated as lad or hood or vagabond or rascal or b*st*rd.
The "Murakami Suigun" were one of the major Japanese feudal navies (or pirates) that existed in Japan. This group were based in Ehime on the island of Shikoku.
Part of the plot centers on the transporting of 300 "tanegashimas" to Oda Nobunaga. A "tanegashima" was a Japanese style musket/rifle that had started to revolutionize the way battles were fought in Japan in the 1500's.
At the time this movie was set, the early 1560's, the Takeda clan seemed to be on the verge of controlling most of Japan. However the warlord Oda Nobunaga was beginning to amass power. Later, in 1575, these rivals would fight at the battle of Nagashino.
The character Kinoshita Tokichiro was the historical person who would later go on to change his name to Toyotomi Hideyoshi and become a major figure in Japan. He lived from 1537 to 1598. He was of a peasant background and went to work for the warlord Oda Nobunaga.