After a night of hunting down demons, Akira Fudo is astonished to see his friend Ryo Asuka reveal the nature of demons while not even mentioning the difference between them and Devilmen. Going back to the Makimura home, Akira finds Miki Makimura and her brother Tare brutally murdered by a mob. Losing control of his anger, Akira slaughters the mob while crying out in agony. The following morning, not many humans are left and demons lead by leaders including Saylos roam the surface. Akira, losing his human-side after Miki's death eventually has his body usurped by the demon he overtook, Amon. With his great power, Amon effortlessly defeats Saylos while slaughtering anyone in his way. He eventually confronts his archenemy, Ryo Asuka's true form, the fallen angel Satan. However, Satan's psychic power as well as Akira recalling his reason for being human confronts Amon in his mind. Akira fights Amon as Devilman with Amon appearing to have the upper hand. However, Devilman manages to counter and overpower Amon, with Akira regaining control of his body crashing into the ground within a crater in the shape of a giant version of Amon's form. Waking up, Akira meets Ryo but exchanges no words with him as Akira walks away.
- Akira Fudo: The leader of the Devilman Corps and the prime threat against the demon race. After the death of Miki, he inadvertently allows Amon to regain control of his body.
- Amon: The mighty demon warrior, who was happy to kill anything that even slightly agitated him. After escaping the mind of Akira Fudo, he goes on a bloody rampage until he has a final battle with Akira for dominance of their shared body.
- Satan/Ryo Asuka: A beautiful angel who betrayed his/her own race to fight for the demons. Having fallen in love with Akira, his/her actions spurred by jealousy causes the deaths of everyone Akira cares for, which only drives a further wedge between the two.
- Miki Makimura: A childhood friend and love interest of Akira; her violent death at the hands of an insane group of humans is what causes Amon to awaken.
- Kensaku "Tare" Makimura: Miki's younger brother, who meets the same fate as his sister.
- Saylos: A powerful demon with his own personal army. He wants Akira to join his army or die by his hands.
- Mikiko Kawamoto: A female Devilman who can emit powerful acids from her body, she is close friends with Akira and a mother figure to Yumi.
- Yumi: An orphaned female Devilman in her preteens; she acts as bait to help Mico and Akira hunt down demons. She is later savagely murdered by Amon.
- Psycho Jenny: A demoness with immeasurable psychic powers who acts as Satan's aide.
- Zuboo: A frog-like demon with strong morphing abilities; he is drawn out using Yumi as bait and is attacked and killed by Mico and Akira. He seems to prefer targeting helpless young girls.