Kurogane Yaiba grows up in the forest learning the sword from his father Kenjuurou and reaches Tokyo inside a shipment of pineapples, with no idea how a city works. The Mine family takes him in and Sayaka Mine hauls him off to school, where he picks a fight with kendo prodigy Takeshi Onimaru that ends in a draw. Onimaru finds a cursed katana soon after and turns his ambition on the world, which sends Yaiba after legendary blades of his own.