Reliable early local traditions are scarce, and Sazae-oni has been known chiefly through Sekien's picture. A later, widely repeated erotic tale tells of pirates who rescue a drowning beauty with lustful intentions. The woman is really a Sazae-oni, who bites off their testicles and returns them only in exchange for an enormous payment in gold. Often presented as a tradition from Namikiri in Kii Province, the story can be traced instead to the Shōwa-period volume Yōkai, Majin, Seirei no Sekai, edited by Yamamuro Shizuka and others and published in 1977^[3][2].

No direct connection between that pirate story and Sekien's Sazae-oni has been established, and the episode is not confirmed as a tradition predating the modern period. One of the book's editors was Yamada Norio, who is known for supplying stories to many Sekien yokai that originally had none, making modern invention especially plausible here[2]. Any account of Sazae-oni should therefore separate Sekien's original conceit—a tsukumogami inspired by classical transformation lore—from the bawdy pirate story added in the twentieth century. The older image finds its force in a quieter thought: even a shellfish may, with age, acquire a spirit and become an oni.