13 years ago, an unknown object appeared at Shinjuku. That creature regularly gives birth to a demon. Therefore, our world is being eaten clean.
The military found a weapon capable of fighting these creatures, a special power known as "exex" that becomes part of the human body.

Action manga about the German 8th tank company on the Eastern Front of WW2 during the fall of 1943.

As a baby Jiro was delivered to his foster parents by a massive oni, who said he would return for Jiro in 15 years. When the time comes Jiro must contend with enemy oni, dark cultists, and their minions while attempting to protect both his parents and girlfriend from their depredations. Ultimately he must embark on a journey through the past, future, and other dimensions to embrace his destiny as Shuten Doji reborn.

One of the first published works by famed Berserk mangaka, Miura Kentaro. It follows the heroic lone wolf, Noa, in a desert-punk post-apocalypse.

Somewhere in Tokyo, there is a room. In that room is a black sphere. Periodically, people who should otherwise have died are transferred to the room. There, the sphere gives them special suits and weapons and sends them out on a mission to kill aliens here on Earth. While these missions take place, the rest of the world is largely oblivious to them. These missions are lethal and few participants survive them. The sphere calls the shots and it's not the slightest bit nice. Its name: Gantz.

The manga consists of nine entirely separate short stories set in World War II, each reimagining a famous fairy tale with the European theater of World War II as a backdrop, often with poignant results.

(Source: Hokuto no Gun)

A collection of eight Zombie related oneshots by several authors.

And I Love Her by Katsuya Terada
What would it be like to live a life with a zombie grandmother in the basement?

Dead and Fail to Die by Hitoshi Kino
Story about a special section of police in a city plagued by an outbreak of a deadly disease.

Children Living with Corpses by Uguisu Sachiko
In a Japan, where zombies are lurking in streets, the small Mika and Makoto are still human unlike their parents that day after day become more and more hungry.

Zombie by Shimada Toranosuke
During a meeting of former classmates a person reports that their old friend is dead, and that during the wake hid body has disappeared.

Forest of Spirits by Hokazono Masaya
A story of how a young student helps his professor revive his dead wife.

Zombie Boy by Hiromoto Shinichi
Shows us the adventures of an unemployed guy who gets a job as a janitor and finds himself chasing zombies.

Fight of of the Living Dead by Koizumi Tomohiro
During a martial arts fight one of the fighters feels ill and vomits; taken to the hospital, he confided to his friend that he had been bitten by a zombie.

Organic Human Solution Organogel by Fukao Atsushi
Year 2073 - Terrorism has spread everywhere and with it biological weapons. In this scenario, a healthy girl goes in search of hear father from whom she was separated, revealing a horrible truth.

Includes illustrations by Hiroe Rei, Samura Hiroaki and Matsumoto Jiro.

One night, senior high-school second-year Nishina Airi is abducted. When she wakes, she is trapped in an uncanny, isolated space with other students from her high school and forced to take part in the “Werewolf Game”. Thus, a death game filled with fear and terror that would pit “Werewolves” and “Villagers” against each other, force them to murder – a game with rules so absolute, defiance is punished by gruesome death – begins.

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 time travel, aliens and the alternate universe war.

From MangaHelpers:
The world is in a war against an alien race called "Mimics," who have taken over most of the world with a mission to eliminate the human race. Keiji Kiriya is a new recruit in the United Defense Force, which is battling against these "Mimics." On his first day of deployment, Keiji and his unit encounter "Mimics" and are all killed... Or was it all a dream? For some inexplicable reason, after every time he dies, he is resurrected and returned back to the day before the battle. Why does this happen to Keiji and how can he escape from this never ending cycle?

Note: Nominated for the Eisner award for the "Best U.S. Edition of International Material - Asia" in 2015.

First issue of a canceled series; collected (in thumbnails) in Blame and So on (Artbook)

From Anime News Network:

A collection of short stories that look to mankind's exploration of space, and examine the possibilities that we could face when we decide to take those first fateful steps into the unknown.

Inside the jungles of Vietnam, a courageous Special Ops. Unit is fighting the most infamous war of decades past—the Vietnam War. This bold account follows the brave exploits of Sergeant “Perky” Perkins and his unit… of rabbits! Join Rats, Perky and Botaski as they fight against the cats of the Viet Cong. From the Tet Offensive to the My Canh bombing, watch these commando-style bunnies through an anthropomorphic lens as events unfold and violence erupts.

Non-human cast of characters notwithstanding, this compelling and painstakingly-researched work places an emphasis on factualism in order to accurately portray the events of the Vietnam War. With a fresh perspective on one of history’s greatest calamities, Apocalypse Meow is a daring new take on a conflict that won’t soon be forgotten… especially after these young rabbits are done!

Like the earlier Battle Royales, a class of middle school students are picked to compete in fights to the death on an island until there is only one left.
The manga follows the point of view of Girl #10 Makoto Hashimoto, an unlucky girl who fears that her class will be chosen to participate in "the program," a mysterious event that forces students to kill each other. Makoto attends Shikanotoride Junior High School. After the encouragement of her best friend Itou Yamamoto and her mother she decides to face the chances. Her fears are supposedly put to rest when word spreads that all 50 Programs had already been executed in the year making them 100% unlikely to participate....

Man is having a hard time finding food and getting rid of their trash, so science comes up with a bio-engineered animal that survives by eating trash, and is then killed to feed humanity. But the self-replicating, endlessly hungry killing machine gets loose in Tokyo...

Killy is a man of few words. He wanders, seemingly endlessly, through a lonely, gargantuan labyrinth of concrete and steel, fighting off cyborgs and other futuristic nightmares, searching only for something called Net Terminal Genes. And he has a very powerful gun, which he uses without hesitation whenever anything resembling danger rears its ugly head.
Who is this quiet, violent, determined man and what are these Genes he seeks? The small communities he finds tucked into the crevices of this towering, dystopic ruin hardly give him leads on his treasure, driving him to find larger enclaves of civilization where people can reveal more about the world he lives in and the quarry he seeks.

When Shouta finally finds a clue to his missing brother’s disappearance, he mysteriously wakes up in a room he’s never seen before. The events of this room are broadcast online, and the only link with the outside is voice chat with the viewers of the broadcast.

In the midst of this extreme environment, a battle royale style murder game begins!

The third World War is nearing. Each super power country is going through a communications war to prepare for it, a war to obtain the top profiles' information of enemy countries using the Russian's secret weapon BEAR, China's Hao Long, and the United State's Confidential Assassination Troop, a.k.a. CAT.

The series consists primarily of short vignettes detailing the adventures of the Crossbone Vanguard space pirates three years after the original manga.
The first story is set during the One Year War and deals with a young Umon Samon. The series also features the "return" of Grey Stoke, an aged Judau Ashta under an alias, who first appeared in Hasegawa's Mobile Suit Victory Gundam Side Story manga.

Fudou Jun is a highschool teacher and takes a trip with a group of students. While there, a group of martial artists staying nearby take a strange interest in the girls.
These men are actually demons and after changing into their true form break into the cabin to rape the girls. One gets Jun and violates her.
She feels her soul being torn apart and transforms into Devilman Lady. With newfound powers and strength she kills all the demons and protects the girls from any further harm.
What are these demons and why did she turn into a hybrid of one? What does this mean for her and for the rest of humanity?