Akira Fudo is a teenage boy who transforms into the demonic entity Devilman to battle supernatural threats. As a human, he appears as an ordinary student. In Devilman form, he possesses superhuman physical capabilities: flight through bat-like wings, enhanced strength to tear through mechanical and organic foes, and resilience sustaining combat despite severe injuries. He projects energy beams from forehead antennae.

After uncovering Dr. Hell's alliance with the Demon Tribe, Akira contacts Koji Kabuto. Their initial encounter features Devilman mocking Mazinger Z's flight limitations, sparking a competitive motorcycle race that establishes early rivalry before alliance. Akira’s transformation ruptures his human form, expanding to 2.9 meters while revealing claws, a tail, and distinct facial markings.

During a critical hostage situation, Devilman rescues Sayaka Yumi and Shiro Kabuto from the demon Sirene, showcasing his protective instincts. Koji witnesses this transformation, learning Akira’s dual identity. Later, when the amorphous demon Bugo traps Devilman, Koji reciprocates by saving him with Mazinger Z, forging mutual trust. Akira subsequently reveals his role as a rogue demon defending humanity.

Dr. Hell and the Demon Tribe assault the Photon Power Laboratory, testing the alliance. Devilman aids the defense but is overwhelmed and captured. Demons torture him, crucifying him on an ice cross above clouds for betraying their tribe. Koji pilots Mazinger Z with the repaired Jet Scrander into aerial combat, destroying the Navalon fortress to free Devilman. Post-victory, both acknowledge mutual respect as Devilman departs to confront lingering demonic threats.

The narrative concludes with the characters separating cooperatively, their initial tensions resolved and a foundation laid for potential future alliances.