The story does not end with the serpent dead. Cutting into its fourth tail, Susanoo's own blade nicks on something harder than flesh, and he draws out a second sword from the wound, which he sends up to Amaterasu as a gift and reconciliation offering. She in turn passes it down to her descendants, and it becomes the Kusanagi no Tsurugi, the Grass Cutting Sword, one of the Three Sacred Treasures of the Japanese imperial regalia alongside a mirror and a curved jewel, symbols of legitimate succession still invoked, though never publicly displayed, at an emperor's enthronement. The Kojiki and Nihon Shoki differ on small points, including the sword's original name and exactly how the vats were arranged, differences textual scholars use to reconstruct which regional or courtly traditions each compiler drew on.
Modern interpreters have read the myth several ways at once: as a folk memory of flood control works taming the Hi River's destructive floods, given the serpent's described belly of "always inflamed and bloodied" red clay-like ground; as a political allegory for the Yamato court's absorption of Izumo, an older and rival regional power, into its mythic and dynastic order; and simply as a hero-and-monster tale structurally close to the dragon-slaying stories found across Eurasia, sharing the pattern of stratagem overcoming brute size that recurs from Near Eastern to Norse myth.