Samejima, nicknamed "Samejima the Invincible," is a Yankee who relishes combat, but his Achilles' heel turns out to be Toraji, the best friend of his younger sibling, and the only adversary he's unable to conquer. Although he persists in his assurance that he'll one day defeat Toraji, why does he find himself powerless to resist when Toraji utters the endearing nickname "Naru-chan" in his ear?