In the event of Inuyasha’s birth, the suitor Takemaru kills Lady Izayoi, just before Inuyasha’s father arrives. Still injured from his battle with Ryūkotsusei, he resurrects Izayoi with the Tenseiga, telling her to escape with their son, whom he names Inuyasha, and gives her the Cloth of the Fire Rat to protect them from the burning and collapsing palace, where Inuyasha’s father died facing Takemaru with his third sword.
In the present era, Kagome’s grandfather comes by with a sword which he calls a “national treasure”; as Grandpa is about to put it in the storehouse for “safe keeping”, Kagome’s younger brother goes over to the sword and it speaks or more accurately, the spirit of the sheath, Saya. With his seven hundred-year spell on the sword So’unga failing, Saya seeks out Inuyasha, hoping he has the willpower to control the sword. Unfortunately, he was mistaken, as it tried to possess Inuyasha, but he tried his best to resist being controlled and finally brings the sword back to the past, but in the process unleashes the deadly Dragon Twister on an evacuated village, a technique far more powerful than either the Tetsuseiga’s Backlash Wave or the Tokijin’s Dragon Strike. Sesshomaru is alerted to the return of So’unga and follows the scent to find that InuYasha is possessed by the sword. The two of them duel and at a crucial moment, Kagome, having returned with Saya, saves the day and forces the So’unga to release Inuyasha from its grasp. As Inuyasha and Sesshomaru depart their respective companies to seek out So’unga, Myoga, Totosai and Saya explain to everyone that in the aftermath of Inuyasha’s father’s death two hundred years ago, they carried out his last command for his three swords. While the Tetsuseiga and Tenseiga were taken care of, Saya claimed that there were no instructions for how to dispose of So’unga. Unable to give it to either Inuyasha or Sesshomaru, Saya decides to keep So’unga asleep for at least seven hundred years and had it thrown into the Bone Eater’s Well, where it ended up in the possession of Kagome’s family.