The Honjo Masamune is regarded as the finest sword ever forged in Japan, made in the 13th century by the swordsmith Masamune and kept for 250 years as the ceremonial blade of the ruling Tokugawa shoguns. This episode of Myth Hunters traces its path from shogunal treasure to national relic after the Tokugawa fall from power in 1868, then follows the trail into the chaos of postwar Japan, where the sword vanished after being surrendered under Allied occupation orders disarming Japanese households of edged weapons. Historians and sword experts walk through Japanese archives, museum collections, and swordsmithing workshops to explain what made Masamune's work distinct from rival smiths like Muramasa, and to weigh the competing accounts of who took the blade and where it might have ended up. The film treats the disappearance as an open case rather than a solved mystery, laying out the documented last sightings alongside the theories, without pretending to a resolution the historical record does not support.