The Flag Of Oxalis: Biography Of Chousokabe Motochika

From MangaHelpers:

Set in Tosa on the island of Shikoku, this historical manga tells the story of Chosokabe Motochika. Starting in 1560, the story starts with Motochika and his father Kunichika orchestrating their revenge on the Motoyama clan. Motochika would go on to become an important figure in history, following his dream to unify Shikoku under his rule. [tethysdust]