Daisuke Ōzaru is the father of the young protagonist, Sasuke. He is a highly skilled ninja belonging to the Sarutobi clan, which remains fiercely loyal to the general Yukimura Sanada following the clan's defeat in a 17th-century war against the shogun Tokugawa Ieyasu.

In the wake of this conflict, the victorious Tokugawa orders his chief ninja, Hanzo Hattori, to eliminate all surviving members of the Sanada and Sarutobi factions. Daisuke is injured in one of these attacks but manages to return to his family home disguised as a wandering traveler. However, assassins track him there. In the ensuing confrontation, Daisuke's wife is killed by Hattori's daughter, Kaede, as she attempts to defend her family. Sasuke, who does not recognize his wounded father, witnesses or is otherwise impacted by this tragedy and is forced to flee from Hattori's warriors.

Throughout the story, Daisuke journeys alongside his son. Despite caring for Sasuke deeply, he adopts the demeanor of a strict ninja master rather than a nurturing parent. He teaches the boy various combat techniques of the Sarutobi clan warriors and, on occasion, intervenes secretly when Sasuke's life is in mortal danger. His primary motivation is to protect his son from their many enemies while ensuring he has the skills to survive, but his harsh and unapproachable behavior creates a significant emotional distance between them.

As the narrative progresses, Daisuke falls in love with a widow. Sasuke, still grieving the violent death of his mother, initially resents this new relationship. The conflict between father and son endures until the final episode, when Sasuke finally comes to accept the situation and reconciles with Daisuke. In terms of abilities, Daisuke is acknowledged as a very capable ninja, possessing extensive knowledge of the Sarutobi clan's combat techniques, which he methodically passes on to his son.