From MangaHelpers:

Natural selection has created a deadly new species known as "Eclipse," who are driven to eliminate humanity. A scientist called Kurusu Kenji headed an organization whose purpose was to fight these deadly creatures of bone. To this end, he created the "Osteon," Eclipse-like creatures that obey the commands of the human from whose DNA they are created. Now Kenji is gone, and his assistant Kidogawa Rokuko is attempting to recruit his estranged teenage son. Kurusu Akira wanted nothing to do with the father that he believed abandoned him, but attacks from Eclipse force him to accept his own Osteon from Rokuko. He slowly finds himself drawn into the organization, whose members expect him to take his father's place. Akira and his Osteon may have little interest in protecting humanity, but they are determined not to be beaten! [tethysdust]

Alternative world where Japanese culture kept its ground to this day and further. Protagonist, a female entertainer typical to Japanese traditional customs, finds herself swept into the world oh so familiar, and yet so different from the one she lived in so far.... a world where she has to fight to survive.

Fate/Zero takes place ten years before the events in Fate/Stay Night, detailing the Fourth Holy Grail War in Fuyuki City.

Sengawa's day job is as an accountant working for the police. But at night, he transforms into a ruthless assassin bringing death to anyone who deserves it. Those who have been wronged and whose grievances the police can't - or won't - listen to, turn to The Man With A Thousand Guns to avenge their suffering.

The year is 2028, location in New Koshigaya. A young boy, Isurugi Neru, lives in a poor family and is forced to quit school so that he can find his own way in life. Neru on the other hand, only thinks of one thing: to take revenge on Yagami, a classmate, who's especially gifted and has humiliated Neru numerous times.

Etou Kai may look like a squeaky-clean kid, but the Greater Kanto Narcotics Control Division's new investigator hides a violent alter ego and a dangerous past.

With his stoic partner Kurabayashi Hal, Kai is assigned to track down and stop the distribution of Dragon Speed, a dangerous new drug. But Ryuugen, the syndicate trafficking the drug, is almost impossible to infiltrate. Add street violence and a jurisdiction war with the Meguro Police into the mix, and it looks like Kai's in for some very long days at the office.

From Tokyopop:

Three years after the popular video game The World was shut down, Tokio Kuryuu cannot wait for The World R:X to come out. Unfortunately for him, he forgets to reserve a copy and finds himself with no access to the game. That is, until a mysterious new transfer student forces him into the game and makes him her servant.

G.U.+ follows the player Haseo, a powerful PKKer known as "The Terror of Death". Haseo is obsessed with an infamous PKer known only as "Tri-Edge" who attacked a close friend of his sometime in the past. The manga details Haseo's search for Tri-Edge, and his eventual inclusion in a mysterious group known as "G.U."


Back story of the ps2 game (same title)
In 2015 a fire at the main CC Corp. building resulted in the loss of a lot of data, and The World was forced to shut down. By splicing in data from what would have been another game, CC Corp was able to rebuild the game system. The next year, "The World R:2" was released, but many old players objected because they were unable to bring over their old characters. However, many new users were drawn in by the new style, and over 12 million copies were sold. Though not a match for the previous version's 20 million users, it became the top-selling netgame on the market." As a result of the new world, four major clans (Kestrel, Lunar Tree, Canard, and Raven) came to power. The clans actions shape 'The World', and most players end up taking one side or another during conflicts.

From MangaHelpers:

On his seventeenth birthday, Amamiya Kota was going to ask his classmate Misora Hiyori out. Tragically, he dies in a car accident but is given a second chance back in the living world on borrowed time. He gets entered into a competition called the 13 Game where other people like Kota who were supposed to die return back to the world and given an option: locate and kill 13 other players or suffer the fate of death. Each player is assigned to a handler, mysterious beings with special powers, who use them as if they were characters in a video game. Kota’s handler, Merume, explains that there are players like him all over the country, each with a unique ability that helps them kill, and Kota has to kill 13 players within 1 year. With his demon hands ability that was inspired from his hobby of magic tricks, Kota must unwillingly participate in this cruel game if he wants to live. [vyc]

Seducing the guests to make them pay the most, that is the job of a host. Takashi, currently the No. 1 host, is an apparent professional when it comes to being a host. Being a host isn't Takashi's only job. The Persona XII, guided by the stars are to preserve the balance of fate. The eyes on an assassin serves the guidance of the stars.

Satsuki Kakeru lost his sister by suicide and has been living a dull life ever since then. One day, he is transported into a bizarre world "Red Night" along with his friend Minase Yuka and six other classmates. In order to survive and escape from Red Night, they must defeat six black knights in order to return home.

Thief Gintonic seeks the mysterious treasures known as "The Three Hearts". One night a mysterious woman falls from the sky claiming to be an escaped Princess from a sacked castle. As fate would have it, she has one of The Hearts. But is she really who she says she is? And will Gintonic let her live to fulfill her mission?

Humanity, having faced extinction at the end of the 20th century, would not have entered the new millennium if it weren't for them. In 1969, during their youth, they created a symbol. In 1997, as the coming disaster slowly starts to unfold, that symbol returns. This is the story of a group of boys who try to save the world.

Won the Kodansha Manga Award in the category "Best General Manga" in 2001.
Won the Seiun Award for Best Comic in 2008.

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.

From Beautiful Soup:

"1999" is an angsty and widely varied series about a bunch of teenagers. One of them is the son of a drug lord and so as you can imagine, all sorts of shit goes down, surrounded by a backdrop of convoluted and fluctuating interpersonal relationships.

This is a plot heavy manga with some mildly-explicit sexual activity.

MAL:
This plot takes a new twist to Romeo and Juliet's forbidden love. It's July 7th, 1999 in Shanghai and there are two gangs fighting for control. Only in the ceasefire zone do people live in peace. In a chance meeting Xiaoxue, who is part of the Toulon's gang, and Dawu, from the Xianglongji's gang meet by chance and without knowing they are enemies. In the heat of the moment Dawu takes him to a place he has the keys to in hopes Xiaoxue will join him, but is turned down. With a simple kiss he leaves Dawu not knowing they will meet again, but in very different circumstances

From Manga Updates An ordinary high school girl, Lin Seonu, unknown even to herself is actually a woman saint holding ancient power called the "Jade of Bango." On her seventeenth birthday, she obtained the power to see ghosts, and every morning after that she goes to school accompanied by the harmless and lovely ghosts. One day, however, Lin has an abnormal dream, and that evening, she encounters a terrible evil spirit. Shivering in horror, she is rescued in the nick of time by a handsome man she had seen in a dream. He frees the ridiculous power that had been concealed in her. He says that his name is In Mu, and that he is her fiance.

A graveyard in contemporary Israel has an unlikely visitor. The elderly gentleman from Japan, a former news correspondent, lays a bouquet of flowers at the tomb of one Adolf Kamil. For he remembers the tale of three Adolfs: Kamil, a Jew who grew up in Kobe, Japan, the son of a baker; Kaufmann, only child of a German consul stationed at that port city and his Japanese wife; and the Fuhrer with whom the Far Eastern nation made common cause.

Won the 10th Kodansha Manga Award for general manga in 1986 (shared with What's Michael?).

Haizuka just wants to live a normal life, a peaceful life far away from all the trouble he's faced. But as soon as he starts highschool, an encounter with a girl and a strange creature destroys any hope of a peaceful life.

Reika Ryuzaki, daughter of the late diamond collector Yoshio Ryuzaki, is a jewel specialist who fights with knuckles branded as "Krishna" in cases involving bad guys who rob or misuse jewels for their own gains. She has an advantage in fighting as she can summon spirits from certain jewels to aid Reika in making her a better combatant in the field.

From Ivyscan:

The Lord of Sanwa's son Lamkha saves Kanan, who collapsed on the road, and brings her home. In Sanwa, where the Messengers of Heaven or Flying Serpents roam the skies, a legend has been passed down the generations. According to the legend, a Holy Dragon fell from the heavens following a battle against a Black Dragon and was buried in Sanwa. What is the truth behind the legend?