Nagai, Go

Soft-hearted Akira Fudou has always been somewhat of a pushover. When he reunites with his childhood friend, Ryou Asuka, in a fateful encounter, Ryou reveals to him the terrifying reality of his father's research: demons exist and are planning to claim possession of the earth once again.

Eager to help his friend save humanity, Akira agrees to attend Black Sabbath, a party filled with depravity and corruption, to attempt to merge with a demon. A near-death encounter causes him to unify with Amon, a demon feared amongst even his own kind. Together they form Devilman, a combination of Amon's strength and Akira's pure heart.

After uniting with Amon, Akira begins to fight against the demons with his newfound power, desperate to stop the downfall of all human civilization.

[Written by MAL Rewrite]

Devilman

デビルマン

Adachi, Mitsuru

The story is set in a place very similar in appearance to Earth in the Edo period. However, Adachi (the mangaka) regularly reminds the reader all throughout the series that the setting is another planet in the distant future which just happens to look like Earth.

After the death of his mother, Shichimi sets out to join his step-brothers and -sister who live together in Karakuri Tenement, a place provided by the father they have never met. He finds out that each of them had different mothers (all of whom have died), but were fathered by the same man. Not long after Shichimi's arrival, the siblings decide to journey to visit the graves of each of their mothers. On this journey, they encounter many dangers.

(Source: Wikipedia)

Nijiiro Tougarashi

虹色とうがらし

Ishinomori, Shoutarou

The manga version of the live action Robot Keiji tv series.

The story is about a robot named Robot Detective K dressed in a human Detective outfit fighting kaijin.

Robot Keiji

ロボット刑事

Iwata, Kazuhisa

Something monstrous rises up from the sea and nearly sinks a Japanese fishing boat. The sole survivor tells a tale that no one wants to believe. 

But when a Russian nuclear submarine is destroyed in the same waters, the world is forced to face the truth: Godzilla has returned! This manga classic was originally published by Dark Horse in black and white in 1988

(Source: MU)

Godzilla

ゴジラ

Miura, Kentarou

Rick has lived a normal life as a mechanic's apprentice in a world underground. That, however, is about to change as he bumps into a strange intruder who is not quite like anyone Rick has ever seen before. Venus, the intruder, claims to be from another world just like Rick's, though slightly different. With the police after Venus, can they figure out what is going on?

(Source: MU)

Futatabi

再び

Fifteen days following the final war in the Gobi Desert, the desolate biome has become nearly impossible to survive in. With the last flight off of the planet departing in four days, the few remaining survivors struggle to make their way to the port and catch the final flight. Although Jay and Ellen only have three more days of travel before they reach the port, Ellen is beginning to reach her limit as their rations run out. Determined to make sure they both make it out alive, Jay decides to scour an old colony wreckage for supplies.

Elsewhere, a woman named Angel Reagan finds herself offering her body to a group of savage men in exchange for some water for her younger sister. Just as things are about to intensify, the men are brutally murdered in front of her eyes by a man with a body made of metal. Introducing himself as Noah, the "hero" indiscriminately kills any hostile force against him, much to Angel's dismay. But Noah's moral reasoning for his actions slowly becomes clear for Angel the longer they spend time in an environment that brings out the worst in humanity.

[Written by MAL Rewrite]

Kobayashi, Tatsuyoshi

After a terrorist bombing takes the life of his only daughter, reknowned bio-geneticist Professor Shinigami merges her cells with those of her favourite rose in life. When the rose is almost destroyed in an earthquake, he also bonds Godzilla cells, which the Japanese government gathered for study after The King Of The Monsters last raid on Japan, to the plant to make it immortal.
The same terrorists want the G-cells, and threaten to unleash Godzilla once more if the Japanese government fails to give in to their demands.
Soon, Godzilla returns and makes his way towards the genetically altered plant, which has now mutated into the colossal horror called Biollante!

Godzilla vs. Biollante

ゴジラvsビオランテ

Oze, Akira

Yajima, Masao

After having vivid daydreams of a barren and far off world, a teenage delinquent finds himself transported to this world after a near fatal accident.

Ryuu

リュウ

Tanaka, Yoshiki

Katou, Naoyuki

Kamoshita, Yukihisa

In the far future, two young military leaders rise above their peers. The invincible genius Reinhard von Lohengramm is matched only by the unbeatable magician Yang Wen-li; though the two share a profound respect for each other, they meet on the battlefield not as comrades but as bitter adversaries. Commanding thousands of warships and millions of soldiers, they lead giant space fleets into battle on behalf of the two interstellar states that have wrested for control of the Milky Way for over a century and a half. 

The Galactic Empire, an absolute monarchy ruled by Kaiser Friedrich von Goldenbaum IV and an entrenched nobility, seeks to suppress the rebels daring to oppose the inviolable crown. The Free Planets Alliance, a representative democracy led by a corrupt High Council, degenerates as its elected leaders⁠ use war and conflict as a way to win popular support. Reinhard is a minor noble who became a High Admiral through his strategic brilliance and his sister's position as the favored concubine of the Kaiser, while Yang is an avid historian and reluctant commodore hailed as a hero despite only using his tactical prowess to navigate around his leaders' incompetence. On opposite sides of the galaxy, the two men have wildly different visions for the future: Reinhard dreams of uniting mankind under his iron fist, while Yang wants only to carve a path to lasting peace. As the war rages on, Reinhard and Yang each strive for their ideals and secure their place among the stars as the leaders of a new era of galactic heroes.

[Written by MAL Rewrite]

Ginga Eiyuu Densetsu

Legend of the Galactic Heroes

銀河英雄伝説

Otomo, Katsuhiro

Nagayasu, Takumi

Orbiting serenely above a long-ago poisoned earth, the last bastion of human civilization is the space colonies. After a terrorist attack, the colonists are forced into exile on the blighted planet below. In the confusion, a young mother is separated from her family and is flung into a bleak, uncertain future... But Sarah will not rest until she finds her children.

(Source: ANN)

Sarah: The Legend of Mother Sarah

The Legend of Mother Sarah

沙流羅 -The Legend of Mother Sarah-

Matsumoto, Leiji

In the future, humanity has achieved a vast starfaring civilization, but is slowly and steadily succumbing to ennui or despair, often due to defeat and subjugation by a foreign invader. Rising against the general apathy, Herlock denies defeat and leads an outlaw crew aboard his starship Arcadia to undertake daring raids against Earth's oppressors. Their primary oppressors are the Mazone, a race of organic plant-based alien women who explored Earth in the mythic past and are now back to reclaim it.

(Source: Wikipedia)

Uchuu Kaizoku Captain Herlock

Captain Harlock

宇宙海賊キャプテンハーロック

Michihara, Katsumi

Faithful to the novels aside for some changes that may be considered major e.g. characters changed from male to female.

Manga Like 8 Man

Devilman

Nijiiro Tougarashi

Robot Keiji

Godzilla

Futatabi

Noa

Godzilla vs. Biollante

Ryuu

Ginga Eiyuu Densetsu

Sarah: The Legend of Mother Sarah

Uchuu Kaizoku Captain Herlock

Ginga Eiyuu Densetsu