The great demon Mao Dante, exploiting the weakness of a boy exposed to his demoniac influence in the dreams, is awakened from a thousand years sleep.
The will of this being, a survivor of an ancient and forgotten civilization , is to wipe out the whole human race.
Anyhow nothing is so simple: the motivations of the demon aren't so wicked as one could think and they will combine with the life of the boy which hangs between nightmare and craziness.
In the meanwhile the satanist will fight against the hierarchy of the church to obtain a justice which is, as it's easy to guess, that of the demon Mao.
This series didn't have an ending until it's remake in 2002. Nagai took many ideas from Mao Dante into Devilman. (mangaupdates.com)

In the prehistoric times when men were reptiles and the world was over-run with dinosaurs, humanity was threatened with war. The humans are fighting against the almighty Gor to return peace to their world.

It is 199X A.D. In Kushiro, Hokkaido, three bodies of Dragonite appear. Possessing overwhelming destructive force, they attack the city. They also awaken the evil Jashin Drago from the holy seal he was trapped in. 200 years ago, Drago was trapped in the seal by a holy warrior with the tattooed mark of the Liger. Assuming that the warrior is dead, Drago and Empress Zara are free to conquer the Earth using their army of biomechanical beasts. Even the Japan Self-Defense Forces are no match for the Dragonites' awesome power. One of the people fleeing is the protagonist, a milquetoast 16 year old boy named Ken Taiga. Unbeknownst to the Dragonites, Ken realizes that he is the descendant of the Liger warrior. In a burst of anger, Ken's Liger birthmark appears, and he rises his palm into the air, shouting the henshin command, "LIGER!" which then covers him in demonic, long-haired biomechanical armor. Ken transforms into Jushin Liger to fight the evil forces of the Dragonite!
(Source: Wikipedia)

In this story, Nagai gets his folklore on with every chapter containing a lot on Buddhist lore or Japanese folklore. The prologue introduces us to Heaven, Incorporated, a company with a particular staff that hunts down all sorts of supernatural monsters and protects humanity from them.
(Source: MU)

One of Go Nagai's first works, this violent period piece takes place in the 1500s and stars a talented low ranking ninja named Shishimaru. In it, Shishimaru fights against Ginnai Doma (an immortal samurai who, despite being butchered multiple times, doesn't die) because Ginnai murdered his comrades. Despite being set in historical times, it has machine guns/lasers/robots/atomic reactors with no real explaination.
(Source: MU)

Welcome to the Sparta Acadamy, run by a head master called Satan's Toenail. If you get anything below a 90 on every test, they punish you with torturous devices and the like. But fear not, there is one who stands up to this great injustice, in nothing but a mask and high boots. That's right, a naked fighter of Justice, Kekkou Kamen is here to punish the unfair system of the Sparta Acadamy and bring justice to those who study too much!

Mazinger Angels chronicles the adventures of four women who pilot giant robots in the Mazinger vein. The concept is a spoof on the late 70's and early 80's popular TV series Charlie's Angels.
Three of the robots, Aphrodite A, Diana A and Minerva X are from the original Mazinger Z series, while Venus A is from the Great Mazinger series. Their pilots are also traditional characters from Go Nagai's universe, Sayaka Yumi and Jun Hono from Mazinger Z and Great Mazinger respectively, and Hikaru Makiba and Maria Fleed from Grendizer.
The style of the manga highlights the sex appeal of both the characters and the mechas, sometimes similarly to the way Aika's female characters are shown.
(Source: Wikipedia)

Mazinger, later called Mazinger U.S.A. Version or Mazinger U.S. Version to avoid confusions with the rest of the Mazinger works, is a 58 pages long manga created by Go Nagai specifically for the US market. It features full-color graphics, text in English and left-to-right formatting. It is partially inspired by Gulliver's Travels.

The year is 2005. The police, unable to carry out their work, are asking for help from talented private investigators for the most complex and important work.
Among these are Seiko Hayami, who, with the help of her assistant Hisashi Hanyu, will be involved in cases concerning strange apparitions of monstrous beings, which will eventually lead to a confrontation with the Panther Claw terrorist organization/religious sect, who worship the goddess Zora, under the command of the bestial Sister Jill.
Defeating the organization seems impossible, but help is at hand from the android, Cutie Honey. Having seemingly traveled from the 70s to defeat Panther Claw, she resides with Seiko in the form of Hisashi. (Source: Wikipedia)

A short manga version of the UFO Robo Grendizer anime. Released along the anime series, UFO Robot Grendizer follows the adventures of Duke Fleed, the prince of Planet Fleed, who, disguised as Daisuke, a farm worker, fights against the forces that destroyed his planet, the Vegan Empire, also the creators of Grendizer that Duke stole to fight them. While not originaly considered part of the Mazinger series, Koji Kabuto and the Mazinger mechas appear in this series, making it sort of a sequel. Grendizer introduced the concept of a transformable robot and a space mecha, concepts that were later taken into other mecha series. It was extremely popular in Japan, Canada, France, Italy, and the Arab world and has a strong following in those countries even today.

Young sports enthusiast, Yamato Hino hears voices calling out to him and during a thunderstorm, he is brought to a parallel world. In this world is the Kingdom Mu, under attack by the evil Dorado of the Empire of Dinosaurs. Yamato was summoned from the prayers of queen Aila Mu to pilot a statue known as the God Mazinger. Joining the Mu army's ranks, Yamato fights against Dorado and his army.

(Source: Mazinger Wikia)

A Violence Jack one-shot from 2001. What happens when Jack and some bikers mysteriously get sent back into the age of samurai.

Slight retelling of the 2001-2002 Mazinkaiser OVA series.

After the world ended in the original Devilman, Akira Fudo is in hell, seeking the soul of his beloved Miki while at the same time Doctor Hell is beseeching the underworld for power in order to get his revenge upon the hated Mazinger. Akira sets in motion a chain of events that earn the enmity of Hades himself, who'll stop at nothing to avenge the slights Akira commits against him...

A kid hears a voice and suddenly finds himself in the company of a demon!

A young woman makes a pact with her 'fairy godmother' Yaaba to become the mighty Cinderella Knight, a beautiful warrior, to protect her beloved Prince Emilio of the country Ballade from an evil conspiracy led by a mysterious group known as "Murder" and their elite assassin corps, The Spiders.
(Source: HappyScans)

Akira Fudo, who has become the Devilman, the only being who can fight demons; a being possessing the powers of a demon and a soul of a man.

A long time ago, the Earth was ruled by demons. The demons constantly fought each other for survival, but soon found themselves fighting a new race of beings: The first humans. The demons then became imprisoned in ice after a great cataclysm. They would remain there until the ice melted, after which it was said Satan would rise and lead them in Armageddon. That time has come in Go Nagai's Devilman.
source wikipedia