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

Manabe, Jouji

It`s face-to-face confrontation when Kahm stares down her father and refuses to end her relationship with Tetsuya. In retaliation, her father sends a punitive fleet to Earth -- with orders not only to crush the rebellion but to annihilate the entire solar system!

(Source: Amazon)

Outlanders

アウトランダーズ

Shirow, Masamune

The main plot revolves around the Yamata Empire's plan to destroy all the galaxy's negative karma  using a massive technological reactor called the Nāga Generator. Unfortunately, negative karma cannot simply be destroyed, it must be atoned for. However the leader of the powerful mystic Buddhist Fuze Clan plans to stop the destruction of the negative karma which will end up creating the nine-headed Nāga and destroy the world if not the whole universe. To help in stopping the creation of the Nāga, the clan summons a Shinto god known as Susano, the Warrior God of Destruction. The powerful, arrogant, and homicidal god faces challenges. These include the Empire and the clan leader's own daughter, the bratty sorceress Seska, who is possessed by the power of the negative Karma and a powerful magic formula.

(Source: Wikipedia)

Senjutsu Choukoukaku Orion

Orion

仙術超攻殻 ORION

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

Watanabe, Michiaki

Pandora's Box led a cursed existence. Through the curiosity of a woman, evil was unleashed and very nearly covered the world in darkness. Miraculously, humanity managed to seal Maou Kestra back into the box, but only with immense sacrifices. Even without their lord, the demons are still a formidable force that has only grown stronger with time, locked in the abandoned capital of the North, Hameln. Fifteen years have passed since that fateful battle...

Meet Hamel, a travelling minstrel who is so self-centered that he'd sooner cook his guardian crow (and family friend), Oboe, than go hungry for even a minute. Welcome to the world of music and hilarious insanity that is the Violinist of Hameln. Watch as Hamel takes cheap shots at his opponents and bashes pigeons with his giant violin and turns them into dinner.

How WILL the world be saved from Maou Kestra with a hero such as this?

(Source: MU)

Hameln no Violin-hiki

ハーメルンのバイオリン弾き

Kanzaka, Hajime

Araizumi, Rui

Young sorceress Lina Inverse and her dim-witted sidekick Gourry Gabriev travel through a somewhat medieval setting, doing good and fighting evil. Well, by "doing good and fighting evil" I mean "stealing from corrupt rich people and blowing things up".

The stories in this volume are occasional tie-ins to the novels and short stories. 

(Source: MU)

Slayers: Medieval Mayhem

スレイヤーズ

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

Obata, Takeshi

Sendo, Susumu

In a world where djinn rule and humans are enslaved, Toto and Loukir break the seals of the century-old prison of the "gentle genie," Rampou, in order to try and save their country...

(Source: Deja-vu)

Arabian Lamp Lamp

魔神冒険譚〈アラビアン〉ランプ・ランプ

Matsumoto, Leiji

Collection of short, humorous stories by Leiji Matsumoto.

Wadachi

ワダチ

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

Sakai, Takayuki

Time-travellers from the 22nd century return to present day Japan to warn the world that Godzilla will soon return, and his rampage will be so great that the country will never recover. With the help of a non-fiction writer who has accurately guessed the true origin of Godzilla, the people of the future offer to return to the past and prevent Godzilla's birth. However, upon returning to the present they find that Godzilla has been replaced by an even greater threat; The three-headed demon King Ghidorah! How can the world survive without the King Of The Monsters to face this new terror?

Godzilla vs. King Ghidorah

ゴジラvsキングギドラ

Sanjou, Riku

Inada, Koji

1-2. Dragon Quest IV Gaiden: Jigoku no Meikyuu
3-4. DQ I Hiden: Ryuuou Baribari-tai

12 Manga Like Cat's World