Inu no Taisho

The Great Dog Demon was a powerful yokai lord who was known throughout Japan. Never formally addressed with a name, he fathered two sons by two different mothers: Sesshomaru from an unnamed dog demoness, and Inuyasha from a human woman (unnamed in the manga, but named "Izayoi" in the third movie). The Great Dog Demon is first mentioned in chapter 12 of the manga as Inuyasha's father, "a demon dog that prowled the lands of the west". The Great Dog Demon's major foe in the manga was the dragon Ryūkotsusei, whom he could not kill but sealed onto a cliff face with his claw; Myoga calls this battle the "cause" of his death.

In the third Inuyasha film, Inuyasha the Movie: Swords of an Honorable Ruler, the Great Dog Demon survives long enough to save Izayoi and their newborn child Inuyasha; still weak from his battle with Ryukotsusei, he dies defending them from a human foe. The gateway to his tomb is hidden in a black pearl (a mystical gem that creates a path between the mortal and spirit worlds) inside Inuyasha's right eye. Within the pearl, their father's body is shown as an enormous dog skeleton in a suit of armor: his true form, according to Myoga. The sword Tetsusaiga, forged from the Great Dog Demon's own fang, rests inside this cavernous skeleton, protected by a barrier that repels any non-human with malice toward humans.

Because of this, Inuyasha inherits the sword rather than Sesshomaru.