Tokyo teens Kei and Masaru are killed by a subway train but awaken in a room with an ominous black orb that gives them weapons, suits and orders. Fighting bizarre alien monstrosities in a deadly game, will they win their freedom or die for the final time? 
(Source: Dark Horse)

Thought your life was bad? Sometimes, death is worse. There is no salvation, peace, nor god waiting to receive you into their care. But wait, a god? Maybe you are talking about that big black ball stuck in the room with you. Now you are thrown into a game, fighting green aliens and robot monsters for the chance to survive. 
When Kei Kurono is killed, he thus finds himself caught in such a game; a test of his skills, morals and will to survive. His life is not his own, his death spat and trampled upon over and over again. What happens if he does not listen? God knows. 
A word of warning: Gantz is not for the faint-hearted, but neither is it as simple as it looks. Gore, rape and violence is rampant, as are portrayals of greed, violence, and all the ugliness that one sees in society today. 
[Written by MAL Rewrite]

Kurono Kei and his ex-elementary school classmate, Kato Masaru have survived the first two ordeals that the unknown black sphere Gantz has sent them through. Exploding body parts, struggling to stay alive till the last seconds and seeing your fellow comrades fall in a pile of blood and gore are norm to them now. They are aware now that Gantz can call them up along with any new deeds, at any time for another confrontation with aliens. 
Will Kato's experiences in the Gantz world give him the same courage in the real world? With fellow veteran Gantzer Kei Kishimoto currently staying at Kurono's home as his "adopted pet", can Kurono stave off his growing lust for her mammaries? 
What the heck is Gantz? 
(Source: anime-source.com)

Death does not have to be the end; one can live again, but only through beating the game posed by the black ball called Gantz. 
 
On his way home to celebrate his younger brother's birthday, brave and kind-hearted student named Masaru Katou is stabbed to death. He awakes in a small room with a cityscape view in the heart of Tokyo—and he is not alone. To his surprise, it is not the afterlife, but the waiting room for a high stakes game with their lives on the line. Before he has the chance to process the situation, Masaru is handed a gun and teleported into the center of Osaka to carry out one simple task: eliminate any alien on sight. 
 
Accompanied by the aged Yoshikazu Suzuki, the stunning idol Reika Shimohira, and the cold but experienced Jouichirou Nishi, Masaru must overcome his fears in order to survive the game and return home to his waiting brother. 
 
(Source: MAL Rewrite) 
 
Note: A full 3DCG movie adaptation of the manga's Osaka arc.

A group of high-school students had an accident on their way to a trip and died but they find themselves in a classroom with a black sphere.


The story of Nishi and Izumi, before the events of GANTZ.

A special one shot that shows what Nishi does in his spare time.

Oku Hiroya tells in this manga what inspired him to draw GANTZ, and his love of Sci-Fi movies.

The main character is named Nagatomo, he is an astronaut and a scientist in charge of a secret operation about experimenting cryogenics on human subjects such a assasins or political prisoners, all inside a spaceship called "RETRO". Suddenly he wakes up inside the ship only to see outside a huge amount of black spheres floating in space, he first believes they could the debris of something, then he realizes there is life activity inside them and leaves the ship to bring one of those spheres inside, then he proceeds to open it and founds a girl inside it, Kishimoto. 
Suddenly, Kishimoto is transfered along Nagatomo to a GANTZ room that looks like it's the Tokyo one, the black sphere inside the room starts playing the radio song and reveals the target, the "comedian alien", then sends both to the battle area. Kishimoto is wearing her GANTZ suit now but Nagatomo is only wearing his space suit, they fight the aliens (Kishimoto proves to be useful, because she knew about the missions) and are sent back to the room. 
The "Astronaut" gets 6 points and "Big tits" gets 0, Kishimoto decides to stay in the GANTZ room because there is no place she can go back, Nagatomo leaves but not before saying he will be back. 
Source: mangahelpers

The manga's story begins when a peasant named Hanbee asks a girl named O-haru for her hand in marriage, but O-haru confesses that she is already thinking of another man named Masakichi from a neighboring village. When Hanbee seeks out Masakichi, he finds that Masakichi possesses a sword and the skills to use it, despite being a peasant.
 
(Source: Anime News Network)

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