Amon: The Darkside of the Devilman (AMON デビルマン黙示録, literally "AMON: Devilman Apocalypse") is a manga written and drawn by Yu Kinutani. The manga has a non-linear narrative that jumps around several times, exploring different characters and concepts, some of which were only lightly touched upon in the original 'Devilman' manga.
The story begins with Akira Fudo clutching the head of Miki Makimura in his arms after she was brutally murdered by human rioters. Not long after Mico, Meriken-Jo, and Dosu-Roku come together to try and find Akira only to find out that Amon had reemerged as he wiped out several hundred armed soldiers. The trio barely escape with their lives to the home of the Bonds of Hinduism. Dosu-Roku fuses with three other Devilmen to try and reawaken Akira and almost succeed but fails at the last moment and dies in the process. The battle continues with Amon facing off against Zennon. Eventually Satan manages to break through to Akira who is able to regain control of his body before Satan sends his body back down to the desolate wasteland below.
In a time skip taking place either before the previous volume or within the start of a new timeline, a new scenario is given with the ancient past demon race during the Cretaceous era. After an attack by several Tyrannosaurs, the Sirene Tribe find a seemingly human baby with light skin. The mother of the tribe deciding to raise him as one of their own, despite criticism from the black feathered Sirene Sheena. The human grows older and is given the nickname 'White Monster', and comes into contact with the white skinned and feathered offshoot of the Sirene Tribe and helps her gain a full physical body. During this, most of the Sirene Tribe was wiped out by an attack by dinosaurs with Mother giving her flesh as nourishment for the newly born and named Sirene and the Boy. Sheena as the only survivor of the attack discovers that nothing of the tribe is left including Mother. She then finds herself surrounded by Tyrannosaurs and is forced to fight them head on, however she breaks a leg and loses her mighty wings.
Eventually Sheena, the Boy, and the newly named Sirene reunite alongside several other demons who had been brought together by Satan, an Angel who wanted to help the demon race fight against God. Other members of the group are introduced such as Zannin and Kaim. Sheena and the boy are told about the mysterious Deathless Amon by Kaim who says it contained the essence of a mighty demon. Sheena gets to Deathless Amon and tries to fuse with it so she could fly again. Unfortunately, she fails to dominate the consciousness and is absorbed. However she dies happily with illusions of her flying in the sky once again with a new body. Later the boy comes up and successfully fuses with Deathless Amon and becomes the newly powered Amon.
Meanwhile Sirene is kidnapped by a strange group of creatures who mistook her for Satan. They bind and gag her before taking her to the city of Atlantis. Unknown to her she was waiting to be killed by several Angels who were luring or kidnapping female demons and sucking out their souls, replacing them with their own in a sickening sense of purification.
A young demon girl named Atai comes down and visits Sirene who was slowly gaining lucidity after her kidnapping. Atai, noticing she was finally awake confesses to her that she had been admiring Sirene's body for several days only because she found her beautiful unlike her own body that had been partially deformed when she was forced to fuse with Tollg. It becomes apparent that Atai was lured to Atlantis with the promise of removing Tollg from her body which she happily accepts. After Atai left, Sirene attempts to contact Amon, he picks up the signal and chases it to the source.
Sirene having gathered enough strength, escapes her ropes and goes to try and find Atai. When she does however, she sees one of the things that had kidnapped her sucking out Atai's blood. Sirene cuts of his tongue and tells Atai to look around her. Atai realizes that she was surrounded by dead demons, she begins to cry and runs from the gates of Atlantis only to run into Amon and Kaim. Sirene is crucified and several of the creatures try to suck out her blood but she uses her powers to cause them to inflate and explode. This annoys the Angels who come down and form together into a perfect copy of Satan. The faux-Satan attempts to deceive Sirene, but its swiftly destroyed by Amon. Shortly thereafter the real Satan arrives leading into a confrontation between the him/her and Amon. In the ensuring chaos Sirene, Kaim, and Atai all fall back to the real Earth.
With both Amon and Satan having disappeared the demons become lost, Sirene becomes despondent, Kaim and Atai become close, and Zannin returns leading a small group of demons. Eventually a bridge appears to God's land allowing for all the demons to enter. Once they do they encounter a strange thing sitting atop a beastly mound. The creature announces itself as Ashura and the mound is a part of Amon's Moon. Ashura promises the demons the chance of great power if they were to fuse with the Moon fragment. Several of Zannin's group do so, only to get fused into it. Despite this Ashura is heralded as the new saviour of the demon race.
It quickly becomes apparent however that Ashura has ulterior motives as he poisons Atai and begins controlling her mind, commanding her to go and kill Sirene and take her wings. This results in a short battle with Atai being regrettably slain by Kaim in the outcome. Sirene begins to weep for Atai, unknowingly calling out for Amon in the process.
- Amon: A mysterious and incredibly powerful demon considered a "Hero" among his race. Although, he didn't care for the human race or demon race often caring more for himself and a few select individuals close to him, and even then he showed affection coldly. He was able to battle and kill the strongest of demons, however thanks to Satan he was placed in dormant hibernation in the body of young human teen Akira Fudo. Due to the death of Miki Makimura, Amon is released and goes free on a blood fueled rampage.
- Akira Fudo: The strongest and most powerful of the Devilmen. He merged with the demon Hero Amon and battled against the demon race however as time goes on his doubts about the human race were commonly prominent and eventually after the death of the girl he loved he loses control and allows Amon to retake control.
- Sirene: A beautiful female demoness, the last surviving member of the Sirene Tribe, she is a lot more compassionate and vunerable then her original version, she grows in maturity over the course for the story.
- Dosu-Roku: Originally a young gang thug, he forms a close relationship with Akira after he saved his life and becomes one of the first members of the Devilman Corps. He proves to be braver than even the eldest of Devilmen when his gives his life to try and rescue Akira.
- Satan/Ryo Asuka: The son of God and traitor to the Angel race who rescues the demons from eradication, after seeing what humanity had taken over the world after years of hibernation he becomes angered and tries to eradicate them similar to how God tried to kill the humans when he realizes this it was too late and Akira Fudo was killed at his hands.
- Miki Makimura: Akira's long time friend and the girl of his affections, with her death he loses control of his demon side and allowed Amon to take control of his body.
- Ashura: A fusion of two Angels condemned for his horrific appearance and a hatred for the demon race. He tries to wipe them out with what he called Amon. One side was calm and collected whilst the other was quick to anger and impatient, he hated beauty in others.
- Cadney: An insane psychopathic Devilman who believed himself to be the only true and pure Devilman and that all others were demons thinking Akira Fudo's reign to be nothing but lies, he took pleasure in the pain of others and was obsessed with his appearance and was either bisexual or homosexual.
- Kaim: A large pachyderm like demon who was strong, noble and brave. He cared deeply for his friends and was in love with Sirene. He was more than willing to give his life for her, the demon Atai seemed to become close to him although Kaim's true feelings never diverted from Sirene.
- Atai: A perky female demoness, whose only real hate in life was her body which had been ruined when the demon Tollg had forcibly fused with her against her wishes. She wanted to rid herself of this and made friends with Sirene and Kaim, originally with the ulterior motive of fusing with them to change her body but ended up forming a close relationship with Kaim, she is eventually possessed by Ashura and sent to kill Sirene where Kaim is forced to kill her.
- Sheena: The black winged leader of the guard of the Sirene Tribe. She was dewinged and left homeless in a dinosaur attack on her nest, she attempts to regain her glory by fusing with Amon but is sadly killed in the process and dies in the process, out of respect Amon closes her eyes so she could rest in peace.
- Mother: The original Sirene and birthmother to the tribe. It was her decision that Amon should be raised as one of their own and raised Sirene in secret to be the best of the Sirene race.
- Zannin: A strong demon who wanted to live in peace and was angered when things got in the way of that, he like Kaim was shown to be brave and noble to protect his own.
- Mikiko Kawamoto (Mico): A female Devilman who was kidnapped by Dr. Rainuma and experimented upon. She was childhood friends with Dosu-Roku and the two confessed their love to one another before he died.
- Dr. Kouzo Rainuma: A scientist and the leader of the Demon Busters he created their weaponry and was responsible for much of the Devilman killings. Not inherently evil and believed he was only doing so to help the human race, motivated only further when his family was killed by demons.
- Meriken-Jo: Dosu-Roku's best friend and another of the gang, he backed up Dosu-Roku in his argument that they should not kill Amon and instead try to save him.
- Masa Bokuto: The gang leader, a brave and noble teen who died when trying to stop a hoard of insane humans from murdering the Makimura children, it was sadly in vain however and they are all killed.
- Manjiro: The youngest of the gang. He fought with a bike chain and was murdered by a demon who posed as a child whom he had previously shown kindness to, he however successfully fuses with it and temporarily becomes a Devilman to try and stall Cadney temporarily.
- Tetsuya: Another of the gang members who was smarter than his appearance suggested. He was slain by Cadney.
- Massami Izumi: A canine like Devilman who fused with the demon Puffurle, she was kind and caring only wanting the best for people and had a good knowledge on religion.
- Zennon: A highly powerful demon who served as Satan's second in command. He tries to stop Satan from falling in love with Akira Fudo but to no avail.
- Psycho Jenny: A powerful psychic demoness who, like Zennon, tries to stop her master from falling in love with Akira to no avail.