Striving to become a true samurai, Yaiba Kurogane was training hard in the jungle. By chance, he returns to Japan and finds refuge with the Mine family, who have ties to his father, Kenjuro. Sayaka, the daughter of the Mine family, begins to live with the eccentric Yaiba, though she is initially bewildered by his ways. One day, Yaiba visits Sayaka’s school, where he has a fateful encounter with the skilled kendo practitioner, Takeshi Onimaru.
Afterward, Yaiba and Onimaru clash repeatedly, and in response to their search for strength, an ancient power begins to awaken. "Raijin Sword" and "Fujin Sword" — the magic swords that have shaken the heavens and earth since ancient times are now stirring once again, and the true story begins...