Inuyasha the Movie 4: Fire on the Mystic Island (2004)

50 years ago, Inuyasha was marked with a blood scar on his back, and as of yet, he hasn't gotten revenge. He encounters children with the same scar desperate to find a way to escape. Inuyasha and his friends is taken to an island by the only child who's escaped. Now, none of them can leave until four war gods are defeated, which seems pretty impossible.