In the turbulent Middle Edo Period, the Unabara State serves as a haven for fierce martial artists consumed by the pursuit of power through battle. Washitzu Naosata, the formidable ruler, seeks his heir among his 31 sons by tasking them to find the most formidable warrior. Each son must nominate a champion to engage in a brutal contest until only one victor remains. The successor will be the one whose chosen warrior stands as the mightiest in the land. Amidst the rugged mountains lies the dojo of the renowned 'Daigame Ryuu' (Giant Tortoise Style), home to Kurogane Gama, son of the legendary swordsman Kurogane Jinsuke, famed for defeating a thousand Unabara martial artists. Washitzu Naosata's son, Washitzu Naoshi, ventures to find the missing swordsman but encounters Gama instead. Impressed by Gama's prowess, Naoshi invites him to join their cause. Eager to hone his skills, Gama embarks on a journey to prove himself as the ultimate warrior.