The sword So'unga, (which can translate to, "Amassing Cloud Fang") was not created by Totosai, nor was it forged from one of Inutaisho's fangs. The initial origin of the sword remains shrouded in mystery. What is known is that the sword is possessed by the spirit of an ancient demon dragon from hell. How Inuyasha's father came to acquire the sword is also unknown, but it is possible (if not likely) that he was selected to wield the sword as a means of controlling So'unga (like Sesshomaru controls the spirit of the Tokijin).
This anime film is located chronologically after the episode of A Strange Invisible Demon Appears! (2003) and before the episode of An Ancestor Named Kagome (2004) from Inuyasha (2000).
The anime film was dubbed on Spanish in Venezuela.