In the feudal era of Japan, Ogami Itto is the elite executioner for the Shogun until the ruthless Yagyu clan frames him in an attempt to gain the position. His name dishonored and his wife murdered, Itto and his infant son Daigoro wander Japan as an assassin for hire, named Lone Wolf and Cub. Ultimately, Ogami Itto strives for revenge against the Yagyu clan.

The devastation caused by the Kantou Hell Quake sunk the buildings in the center of Tokyo deep beneath the waves. A great number of human lives and and a great deal of property sunk along with them. There's no shortage of people aiming to claim these sunken valuables. Many of those people are pirates, who arrived from overseas in salvage ships of unknown nationality. Every night, these pirates raid the chain of small islands, which all that remains of the Kantou region, and assault the survivors.
However, there was no one who was able to stand against the pirates! It was a completely lawless zone. It was Japan, but not Japan: A land and a people completely forsaken by their country.
That is, until Violence Jack rises from the ocean to help the islands' inhabitants fight the pirates and their allies, the New Shu Army.

While Professor Saotome completes his masterpiece, the Shin Getter Robo, a strange object enters the Earth's atmosphere. Hayato, in control of the lab while Saotome obsessively works, orders Getter Robo and Getter Robo G to launch and destroy the object before it impacts.

Stardust Memories is a short story compilation of human beings in the distant future where we have traveled deep into space. Each story describes a moral dilemma that people traveling in space may experience which is something that we have yet to determine in the current world.

Stardust Memories talk about such problems as the implications of having people travel for years, even decades, in the cold, quiet and endless universe. A different story tells on how human presence in a foreign galaxy will affect the environment. The topics the author decides to write about are interesting and makes you wonder about the future.

12-year-old Midori is the constantly abused chore girl for a freakshow. Things begin to change for her after a dwarf magician joins the freak show, but not always for the better.

The world was turned by the "Ice Witch" into that of snow, starvation and madness. Freezing people naturally seeked flame. The "blessing" that was bestowed upon Agni, is it a hope or maybe a curse?

Years after the events of Getter Robo/Shin Getter Robo, Hayato Jin is the leader of NISAR; a private owned research and weapons development organization based in Japan. He, and Professor Tachibana, have been developing various weapons and building up their forces to deal with a threat that started fifteen years ago: the mad scientist Rando. When Rando's forces begin their terrorist operations around the world, NISAR begins its search for exceptional soldiers to pilot their super weapon, the Getter Robo.

Is this a dream? Reality? Or maybe something else...?
Every night, a mysterious man who styles himself Peter Pan sneaks up in Manami's room. He takes her with him to Neverland, an eerie place created out of human desire. Neither pain nor obligation exist in this place. A fairytale land of freedom, where people live governed only by their own instincts. There, all of reality's troubles and unpleasantness may be forgotten. However... being human may not be quite as bad as it sounds.

Volume 1 : The Laughing Vampire.
While a young boy, just resurrected as a vampire, commits acts of awful ferocity, the city around him shows all its perversion. The adults abuse their power, the boys degenerate and use all the available means to achieve their goal to give vent to their low instincts. Whoever can't understand and make opposition is doomed to change or becoming crazy. So which is the real horror? The vampire who kills in order to feed himself or the crawling disease hidden in society, which slowy corrupts without being noticed?

Volume 2 : Paradise.
Following the events narrated in the first volume, Luna and Konosuke are now living together with the old woman vampire as fellows, as lovers, in a diabolic innocence, killing for quieting their thirst for blood, joining death and love under the dream of eternal youth. Meanwhile, a young boy named Makoto is looking for his lost sister Miko, who disappeared years ago in mysterious circumstances. But what really happened to that girl who liked eating grubs and dreamed of becoming one of them? And is there really a terrible secret that someone is hiding? The paths of all the characters will dramatically collide, bringing unexpected consequences after the things are gradually revealed.

A story suspended between weirdness and decadence, showing a clear nostalgia for German cinematography and Federico Fellini, where blood is used to trace a great and only apparently amoral story.

"There are men who, on coming to places that women find unlivable, are all the more determined to find there a reason for living. These men epitomize grandeur."
Welcome to Gun Frontier.

In the panic surrounding a worldwide pandemic which kills 15 percent of the population and cripples many more, a secret organization, the Propater, topples the UN and seizes control of much of the world. A boy and a girl, raised in an abandoned virology research center, immune to the virus, are attacked by the Propater and escape.

Based strongly on Gnostic mythology, all major characters are named after gnostic deities, and have analogous roles.

A tale of obsessive love and constant pursuit, told over a 1000 years.
Escaping from a brother who had just ascended the throne, Yoshitsune, along with his servant, comes across a house in the middle of a desolate mountain. Oddly enough, only a young woman lives there, who seems to possess a very dark and ominous past.
This long journey of more than a thousand years focuses on our main protagonist Kurou. It can be somewhat confusing at the beginning, but once you understand the plot this story can be quite entertaining.
The main thrust of the story goes like this: Kurou meets a beautiful woman by the name of Kuromitsu, and begins a relationship which transcends life and memory. Kurozuka tells the tale of a journey undertaken by immortals, and those who chase after immortality.
The majority of this story takes place many centuries in the future, after Kurou has been separated from Kuromitsu. Having lost almost all of his memories, Kurou seeks to understand why he cannot die, to rediscover his identity, and to find the woman that haunts his dreams.

Lucius Lucent is a cold blooded female warrior that makes men in battlefields quiver in fear. Along with her magical armor, Gil, she destroys everything in her path with her overwhelming power.

A high-school student named Yu Komori is bitten by a radioactive spider, which gave him spider-like powers. Yu faces Japanese versions of villains such as Electro, the Lizard and the Kangaroo. Yu also has an Aunt May (her name is "Mei"), and the publisher of the Joho newspaper is a counterpart to J. Jonah Jameson.

Note: 7 out of the 13 Japanese stories in total were fully translated by Marvel, with heavy edits to remove the violent scenes. After that the title was cancelled, which was a likely decision by Marvel since the stories written by Hirai departed even further from the source material, and included scenes of sexual and gruesome imagery of a kind not seen in the original US comic.

From Brolen:

This is a horror/sci-fi story about a giant planet consuming creature from another dimension that a scientist discovers and mistakenly identifies as a planet. Being given the honor to name it as its discover, the professor chooses to name it after his only daughter, Remina, but when Hellstar Remina is headed on a direct collision course with Earth the world goes nuts and all the people in the city start a witch hunt to kill Remina, thinking she is somehow to blame.

Partake in the horror, the terror, the bloodcurdling madness of the serial killer mind, and the one who dares exterminate them! Except it's a comedy horror. Anyway, contains explict blood and gore, so you have been warned.

-Taken from Iryuu.net

From Yen Press:
A mysterious illness is spreading rapidly through the halls of Fujimi High School. In a matter of hours, the campus is transformed from a place of learning into a hive of nightmares, as the infected students collapse and are reborn as flesh-hungry zombies! Only a handful of students escape the initial outbreak — among them Takashi Komuro and his childhood friend, Rei. He manages to protect Rei from the initial onslaught, but how long can Takashi and the other students hope to survive when the whole school – maybe the whole town — is out for their blood?!

From MbE:

Two brothers who were abandoned in the deep of a cold mountain range. The older brother, Tyltyl, is a slut that sleeps with men for just two pieces of tobacco, while at the same time waits for the father that once abandoned them. The younger brother, Mytyl, holds strange emotions towards his brother. Is it because they’re only half related...? Or is it something completely different...? While holding such feelings, one day the both of them find a fallen soldier. A land covered in snow where time has stopped... Even so, days pass ever so quietly. Many people pass through among the seasons. The place at which souls arrive upon agreement is...?

A selection of short stories. The stories deal with the same themes as Parasyte and his other work, and in only one of them is his art style noticeably more primitive.