Ninja Chronicles: The Legend of Kagemaru

A historical manga that depicts people who defy fate and live by faith in a world of war.

(from MangaUpdates):

The classic, long ninja saga. Many intertwined themes and many characters. It is a series that is as well a traditional samurai tale as an attempt of Shirato to uncover the role of revolting peasants in feudal Japan.

It was adapted into a film by Nagisa Oshima in 1966.

Kagemaru is a fictional samurai, the hero of the story, aiding the peasants in their struggle for life. Nobunaga Oda, the historical 16th century warlord is his opponent.