Sadamune, commonly known as Hikoshirô, is thought to have been either the real or adopted child of the swordsmith Masamune. Sadamune was from Sagami Province (present-day Kanagawa Prefecture) and was active from the end of the Kamakura period (1185-1333) into the Nanbokuchô period (1333-1392). His style resembles Masamune's but is gentler and more regular. The tempering pattern on the blade is an irregular wave (J. midare) type. The sword was given the name "Tortoise-Shell Sadamune" (J. Kikkô Sadamune) because the engraving on the tang-a chrysanthemum within a hexagon-resembles a tortoise shell.
The branch of the Tokugawa family living in Owari Province (present-day Aichi Prefecture) presented the sword to Shogun Tsunayoshi (1646-1709) in Genroku 11 (1698).