The Sengoku Era was a century-long period in Japanese history that was known for its military conflict among social and political upheaval. Warlords ruled, and of the country's leaders fought each other in a never-ending battle to claim both power and land. This was also the era known as the Middle Ages, and the more medieval setting allowed for the impression that various ancient and mystical elements still exist in the world.
In the closing years of the Sengoku Era (late 1500s), Japan was consumed by perpetual conflict. The fires of war raged on, spreading deep into the mountains, to the land of Ashina. Master swordsman, Isshin Ashina, staged a bloody coup and wrested control of the land. In single combat, he defeated General Tamura, and it seemed like the war might finally be over.
In the aftermath of the deciding battle, master shinobi Owl came across a small child. When the child calmly grabs his blade after Owl draws it across his face, Owl is impressed by his fortitude and takes him in as his own son, naming him "Wolf." Training the child over twenty years in the ways of shinobi, Owl assigns him the duty of protecting his new master: Kuro, a child and descendant of an ancient and mystical bloodline. As Owl departs he reminds him of the shinobi iron code: his father's rule is absolute; his master's rule is a close second; and, in the event of his master being kidnapped or placed under threat, he must protect and return him at any cost.