Mazinger Z vs. Devilman

Story

The film begins with the Super Robots Mazinger Z and Aphrodite A defeating three of Doctor Hell's Mechanical Beasts. The battle inadvertently frees the female demon Sirène from underground, and she flies away. Akira Fudo, who witnesses her escape, transforms into his true form of Devilman and pursues her. Doctor Hell, having observed the fight, deduces that Sirène belongs to the Demon Tribe, a race that legend says ruled Earth in prehistoric times.

Using his flying fortress Navarone, Hell and his henchman Baron Ashura follow Sirène to the Himalaya Mountains, where the rest of the demons are frozen. Hell frees some demons and implants mind control transceivers in their chests, striking a deal: the demons will help him defeat Mazinger Z if he helps them defeat Devilman. Devilman, having spied on the conversation, warns Koji about the alliance but mocks Mazinger Z's inability to fly, leading to a motorcycle race between the two teenagers.

The Photon Power Laboratory is developing the Jet Scrander, a winged jet pack, to address the robot's weakness against flying enemies. A demon spies on this and reports to Doctor Hell, who sends Bugo and Sirène to destroy the Scrander. They damage it before being driven off by Koji's ray gun; Sirène takes Shiro and Sayaka hostage, but Devilman rescues them. Koji witnesses Akira transform into Devilman and learns his secret.

Devilman follows Bugo to the sea but falls into a trap, from which Koji rescues him in Mazinger Z. Akira reveals he is a rogue member of the Demon Tribe who protects humanity. The combined forces of Doctor Hell and the demons attack the Laboratory; Devilman is overwhelmed and captured, then tortured on an ice cross above the clouds. Once the Scrander is repaired, Koji uses it to fly Mazinger Z into the clouds, killing the demons, freeing Devilman, and destroying the flying fortress. Doctor Hell escapes, vowing to get Mazinger Z someday.