By the trickery of the Yagyu clan, Itto Ogami, a former “Kogi Kaishakunin” (a professional executioner who cuts the throat of Daimyo after a hara-kiri), loses his entire family with the exception of Daigoro, his 3 year old son. After these cruel murders, Ogami renounces his chivalry with an ardent wish to resuscitate the Ogami clan and take revenge upon the Yagyu. This story is about his various adventures as he departs on a journey as an assassin.

Carrying Daigoro in a carriage with a flag reading "Child and Expertise for Rent. Suio Ryu, Itto Ogami" tied on to it, various dangers accompanied by the evil hands of the Yagyu clan chases the parent and child who have plunged into an awful netherworld.
Watch as they break through the crisis and solve the case with the dynamic swordplay of Itto Ogami’s Suio Ryu (a style of Japanese swordsmanship) and the strong affection between father and son nurtured under severe circumstances.