At the Great East Mine, Kojiro and Tsugumi face an attack from the mysterious swordsman Shiro Inukai, whose sole objective is to steal demon metal blades. Musashi escapes from the abyss and rushes to their aid, but the three friends can't hold a candle to Inukai's strange abilities. Just then, the Obsidian Goddess's power awakens within Musashi! Now's their chance to launch a counterattack!