Fifteen years after the Battle of Kawanakajima, two boys from the snowy region of Echigo secretly climbed up Mount Tsubakuro. One of them was Niijima Kanetsugu, who would later become known as the "greatest retainer in the land." But back then, he was just a young boy who looked up to the glorious military achievements of his predecessors. Soon after, the tides of fortune changed dramatically: the legendary military genius fell overnight, internal strife arose among brothers, and external enemies loomed threateningly... Young Kanetsugu found himself standing in the gap, pushed by history onto the center stage of an era fraught with turmoil and uncertainty.