A man built from the Orochi's own cells comes looking for Tenka, and suddenly the whole foundation of what you thought you knew cracks open. The Yamainu aren't prepared for this, they're fighting pieces of the monster they thought they'd already won against, wearing human faces. Soramaru has to choose between the brothers he knows and the truth about what they actually are, and there's no version of that choice that doesn't cost him something irreplaceable.

Soramaru is attacked by a mysterious man covered in large snake scales who looks somewhat like Tenka and demands to know where Tenka is. Soramaru learns that the attacker was produced by an experiment using cells of the Orochi. The brothers discover that human experimentation, banned after the Orochi was destroyed, is still being carried out in secret to bring the evil snake back. As Soramaru and members of the Yamainu, the military unit formed to kill the snake, search for the truth, they uncover secrets and find former Yamainu members behind the conspiracy. Old friends become opponents, and the three brothers fight side by side once more against the military. The film is the third part of a trilogy adapting the Donten ni Warau Gaiden spinoff manga, with action at its center.