Ogami Ittō, formidable warrior and a master of the suiō-ryū swordsmanship, serves as the Kogi Kaishakunin (the Shōgun's executioner), a position of high power in the Tokugawa Shogunate. Along with the oniwaban and the assassins, Ogami Ittō is responsible for enforcing the will of the Shogun over the daimyō (lesser domain lords). For those samurai and lords ordered to commit seppuku, the Kogi Kaishakunin assists their deaths by decapitating them to relieve the agony of disembowelment; in this role, he is entitled and empowered to wear the crest of the Shogunate, in effect acting in place of the Shogun.
After Ogami Ittō's wife Azami gives birth to their son, Daigorō, Ogami Ittō returns to find her and all of their household brutally murdered, with only the newborn Daigorō surviving. The supposed culprits are three former retainers of an abolished clan, avenging the execution of their lord by Ogami Ittō. However, the entire matter was planned by Ura-Yagyū (Shadow Yagyu) Yagyū Retsudō, leader of the Ura-Yagyū clan, in order to seize Ogami's post as part of a masterplan to control the three key positions of power: the spy system, the official assassins and the Shogunate Decapitator.
During the initial incursion, an ihai (funeral tablet) with the shogun's crest on it was placed inside the Ogami family shrine, signifying a supposed wish for the shogun's death. When the tablet is "discovered" during the murder investigation, its presence condemns Ittō as a traitor and thus he is forced to forfeit his post.
The one-year-old Daigorō is given a choice by his father: a ball or a sword. If Daigorō chose the ball, his father would kill him, sending Daigorō to be with his mother; however, the child crawls toward the sword and reaches for its hilt. This assigns him the path of a rōnin, wandering the country with his father as "demons"—the assassin-for-hire team that becomes known as Lone Wolf and Cub, vowing to destroy the Yagyū clan to avenge Azami's death and Ittō's disgrace.
Ogami's main weapon is the Dōtanuki battle sword. Dōtanuki is a name of a Japanese school of sword smiths from Higo province who produced swords in the Bizen tradition during the feudal period of Japan.
Dotanuki swords quickly gained great popularity among the warrior class due to their superior cutting ability. The Dotanuki smiths cared little for aesthetics, but instead focused on strength, sharpness, and durability in the field. They were renowned for producing blades which would endure the harshest conditions, the most difficult battle field situations and survive to return to battle day after day, year after year.