Ninja Assassin follows Raizo (Rain), one of the deadliest assassins in the world. Taken from the streets as a child, he was transformed into a trained killer by the Ozunu Clan, a secret society whose very existence is considered a myth. But haunted by the merciless execution of his friend by the Clan, Raizo breaks free from them and vanishes. Now he waits, preparing to exact his revenge.

In a remote part of the countryside, a bungled kidnapping turns into a living nightmare for four central characters when they cross paths with a psychopathic farmer and all hell breaks loose.