In 2071, north pole ice have melted and the land has been submerged. Humanity survived but it's divided into two species: the true humans, those who live in underwater cities, and the Dugons, those who chose to undergo genetic modification to live in the sea. Both species go to war to survive as long as the Dugons consider the humans good to eat.

To defend against the Dugons, the city of Mari Ramelle builds a new kind of weapon, the mermaid robot, Salacia. Because of the small size of the the pilot cabin, the robot is piloted by a girl and a boy, both 13 years old: Marin Yuuki and Ushio Mizushiro. The fight for survival is hard, and during the manga, the city builds more mermaid robots.

(Source: MU)

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)

Manga adaptation of Dante Alighieri's classic work "The Divine Comedy".

Join a group of street beggars on their wacky and insane adventures.

The archangel Micheal gave King Solomon a ring with the name of God inscribed on it. Using this ring Salomon enslaved 72 demons and used them to build his kingdom when finished he sealed them in an urn and cast it into a lake. 3000 years later the ring of Solomon is in the possession of a young Tokyo girl named Miki who believes herself a witch.

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)

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.

Although I am a big Devilman fan, and have read a couple volumes of Amon, I am not 100% sure how it ties in with the Devilman continuity. So what I will do is summarize Devilman, and then review Amon. Beware, this review will contain Devilman spoilers, it would be pretty hard to write this without them. Devilman is the story of Fudou Akira, a timid, bullied teenager who is living with his friend Miki due to his parents being away. (They are archeologists.) One day, Akira's best friend, Asuka Ryo tells him he has something urgent to tell Akira and takes him to his house where he explains that demons once ruled the world but were frozen during the ice age. For a long time they were trapped, but now many of them have been freed. Ryo tells Akira that the only way to combat the demon threat is to unite with one. Furthermore, demons can only be controlled by a person pure of heart. Therefore, Akira must unite with a demon to become mankind's savior. With Ryo's help, Akira is able to unite with Amon (Hell's god of war.) and he becomes Devilman. OK, now fast forward to Amon. (Here come the Devilman spoilers.) Miki is dead. Akira's precious friend was killed by the very humans he was protecting. Ryo was actually satan - in human form. The trauma of Miki's death causes Akira to fade into himself and this allows Amon to take over. At the same time, it seems that satan has initiated the apocalypse. (There is this goup spreading from Japan throughout the world, melting/absorbing people.) satan works to bring the demon race under it's(?) (...satan is a hermaphrodite. I can't say "his" or "hers".) control as they run rampant, killing people. The human race, facing the demon threat has entered into martial law and chaos, frequently killing each other even. It seems the world is headed for destruction, and Akira's friends Dosu 6, Mericou-jin (I think I spelled that wrong.), and Miiko along with some other unidentified psychic figures, try to restore Akira's consciousness. While all of this goes on, Amon has only one thing in mind - killing satan. If you can tolerate the violence and demonic themes, Amon is a solid story delivered by the pen of the great Go Nagai with excellent art by Yuu Kinutani. It's not for everyone, but I recommend it to all who are confident they can handle it.

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)

Continuation of the successful manga and anime series Mazinger Z, Great Mazinger starts after the defeat of Mazinger Z. Tetsuya Tsurugi is the new protagonist, piloting the powerful Great Mazinger, a creation of the once thought dead Kenzo Kabuto, the father of Koji Kabuto. This time the enemy is the Mycene Empire and its powerful robots. (manga updates)

A story where students face off against teachers to bring down the tyrannical education system.
(Source: MU)

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...

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.

Slight retelling of the 2001-2002 Mazinkaiser OVA series.

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

One of the first Super Robot manga and the one that introduced most of the traits of the Mecha genre. Constructed with the Super-Alloy Z, Mazinger was built by Professor Juzo Kabuto as a weapon against the Mechanical Beasts of the evil Dr. Hell. Koji Kabuto, the grandson of Professor Kabuto, becomes the pilot of Mazinger Z when his grandfather is killed, and battles from there on against Dr. Hell and his allies. This is the first series that introduced the concept of a pilot inside a Mecha, which all series from then on have followed.

Great Mazinger (Sequel)
Mazinger Angel (Alternate Story)
Shin Mazinger Zero (Alternate Story)
UFO Robo Grendizer (Sequel)
Z Mazinger (Alternate Story)

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)