When high school student Ageha Yoshina finds a red calling card in an isolated, ringing pay phone, he believes he's merely stumbled upon the game 'Psyren', a curious urban legend. He initially intends to trade information about Psyren to the world's foremost fortune teller for a famous reward, but after his childhood friend Sakurako – who happened to possess one of the cards – disappears, Ageha rushes into the game's dangerous world to find him. Now trapped in a post-apocalyptic landscape and pursued by Psyren's deranged inhabitants, Ageha must fight to survive and unravel this world's mystery before the game takes his life.
Kei, a cynical and arrogant high school student, has minimal regard for others; so it's much to his surprise that when he's asked by his elementary school friend Kato to save a drunken bum laying on the subway tracks, he actually complies. However, no good deed goes unpunished, and they are swiftly decapitated by the oncoming train. Kei and Kato awaken in a nondescript room occupied by a black sphere and a variety of other people, and thus begins Gantz's game. In it, the players must face off against aliens in battles where death is inevitable and rewards are minimal. Unfortunately for them, this is just the beginning of their nightmare - at least, for those who manage to survive...
Both Gantz and Psyren begin with normal people being dragged into a deadly, inexplicably game - Gantz's in Gantz and Nemesis Q's in Psyren. The only way out of the game is to survive long enough and earn enough points to get out.
As the stories continue, both sets of characters gain more powerful abilities and eventually stumble on threats to the world as a whole.
Tons of action, monsters and mystery, if you you enjoyed them in one, you are sure to enjoy them in the other.
For no apparent reason, fifteen-year-old Yuri Suzuki is suddenly snatched out of her modern world by a pair of hands emerging out of the water. She is transported back to Hattusa, the Hittite Empire's capitol, during the time of the Bronze Age; its queen, Nakia, wishes to use Yuri has a human sacrifice. The only way Yuri can survive is by becoming the concubine to the Prince of the Empire, and Ishtar to the people of the Empire. With danger at every turn and her heart torn, will Yuri decide to stay in Hattusa, or try to find her way back home?
Living in a town one minute then teleported to this desert like area the next, how will the transported people survive? And if they do survive how will they get back home? The only difference is that the people in Psyren go into the future when Yuri Suzuki from Red River is sent into the past.
In the underground village of Jiha where constant digging is needed to survive, hot-blooded Kamina and little "bro" Simon dig towards the surface in search of a new life. Simon and Kamina's world is forever changed when a gigantic monster called a Gunman drops down from the surface world. Along with the monster drops a young girl named Yoko with a big rifle and even bigger... personality. Kamina, Simon and Yoko escape from the beast to find an odd discovery made by Simon - a small Gunman! Simon pilots the machine with the support of Kamina, and after a grand battle, the three defeat the monster and fly up onto the surface. Kamina and Simon find that the world is being terrorized by these Gunmen, and all humans are being forced underground by their pilots - the evil Beastmen. The three set out to carve a path of freedom for humans from the Beastmen's oppression, meeting new enemies and gaining allies along the way.
In the future, select humans have begun to evolve and acquire special ESP powers – powers that the rest of the populace fear and detest. While some ESPers are harmless, others desire to use their powers for their own personal gain. In order to suppress this threat, identify new ESPers and protect those with powers from the public, the B.A.B.E.L. organization is founded. At its helm are three ten-year-old ESPers: Kaoru, Aoi and Shiho. Together, they will put a stop to crime and attempt to gain the trust of the public; but can their guardian, Kouichi Minamoto, manage to help the girls mature enough so their selfish actions will stop hurting the world around them?
Both titles are shounen, battle oriented mangas about espers fighting each other. Both have a group of children, learning about their powers in special facility (though in ZKC they are main characters, while in Psyren they are only secondary cast).
Both mangas are centered around a prediction for the future disaster, caused by espers (espers raging a war on normals in ZKC, espers turning world into wasteland in Psyren). The good guys, try to stop that prediction from happening.
Generally if you like one, you should check the other as well.