The Tamashi Kunai is a powerful relic and weapon belonging to the Black Spider Ninja Clan for generations. It has the power to trap a soul into itself, human or Fiend, and then channel their power into the kunai's wielder.
Plot[]
Ninja Gaiden: Ragebound[]
After the Fiend Rhyvashi extended an offer to the Black Spider Ninja Clan to help elevate them after their failed alliance with the Archfiend Vazdah and left for the Kû no Tani, Kumo Obaba, the clan's current leader, decided they were going to accept the invitation, but declared it was not going to be as an alliance and stated her intention to have the Black Spider Ninja Clan break the Fiends into submission.
Handing the Kunai
Obaba then summoned the Tamashi Kunai into her hand, and explained its ability to entrap souls into itself and give their power to the kunai's wielder. While its ability to seal had never been attempted on a demon lord before, Kumori volunteered to attempt such a feat, despite it being extremely dangerous. The kunai was then entrusted to Kumori, who set off to the Kû no Tani to make a deal with the Demon Lord.
Unfortunately, it was a trap, and Kumori was captured and pulled into the Underworld. She was held bound in the depths of the underworld, until the wounded apprentice of Ryu Hayabusa, Kenji Mozu, appeared before her. Seeing no other way to escape, Kumori had Kenji take the Tamashi Kunai and impale her with it, binding her soul into the kunai and channeling her power and spirit to Kenji. This saved his life and allowed them to escape the Underworld.
Kenji would retain possession of the kunai for the duration of his and Kumori's quest to stop the Demon Lord from gathering the Energy Crystals needed to free himself from the underworld. If Kenji is chosen to escape the underworld, leaving Kumori behind to face the Demon Lord alone, he returns the Tamashi Kunai to its rightful owners, the Black Spider Ninja Clan.