Yashiro Tenshuu killed 4 people, and is now on death row. However, a secret government organization is willing to take him off death row if he allows himself to become a test subject to an experiment that requires a killer's intent.

From Fantasyshrine:

Since he first met Baron Kuroba, Seiji has been secretly in love with the master of the Kuroba Manor, where servants were rumored to be attacked by a vampire. However, Baron Kuroba only sees Seiji as a lap dog that needs to be disciplined for his carnal pleasures. How can Seiji convince the baron, who doesn't believe in love, to love him back?

This short oneshot tells the adventures of Alice, but with a slightly darker tone.

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]

A collection of short stories:

1. Oral Cavity Infectious Syndrome
On the surreal premise that women's mouths take the often weird shape of their partner's penis, Yoriko starts an investigation to discover with whom her boyfriend is cheating.

2. Local Tourist Information
A guide to an extraterritorial region of Japan.

3. Back Streets in Front of the Station
A girl goes crazy about reverse sides of different things, including streets, cars, and animals.

4. Genesis
Kago Shintarou's rendition of the Book of Genesis.

5. Superglue
What happens when you step on something so disgusting that you never want to uncover it?

6. Akutagawa in Front of the Station
A surreal homage to the writings of Ryunosuke Akutagawa.

7. When All's Said and Done - also included in Hell Season
A gruesome tale of hardened faeces, and a limbless girl.

8. Multiplication
Comic panels are multiplying and create opposing clans.

9. Abstraction
A two dimensional comic about young lovers turns 3D causing the characters' bodies to deform.

10. Blow-Up
What happens when every comic page features exponentionally more panels than the previous one?

11. No Need for Caution
The action of the comic happens outside of the panels--literally--in the white space.

12. The Memories of Others
Everyone's memories become visible via floating comic book panels.

13. Lord of the Ring
An incompetent sumo wrestler uses the powers of a forbidden pair of pants to overcome and shame his competition, until one day someone rises to attempt to crush him and take the pants for himself.

14. Spinning Thoughts
Wearing urinary calculi is the latest fashion trend.

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.

From: Easy Going Scans

If you could find out a little something about the future, what would you do? Get rich off of the stock market? Use the media to become famous as a prophet? Or…

3, Street of Mysteries explores the fantastical-poetic vein that has forged Mizuki's reputation in Japan. The stories contained in this series hold in common the obsessive ideas of immortality and of life after death. Skillfully blending a range of black humor, drama, and questions of morality, Mizuki shows once more his profound understanding of the human soul.

(paraphrased from Astiberri)

There is a mysterious group of people who inflict cruel and fatal games on people for their own amusement. Tatsuya and Misa are out on a date in an amusement park when they wander into one of these horrific competitions on the tallest roller coaster on earth. The seats fall out of their 12-person roller coaster car, and they are told that the game will end when all but one person has fallen to their death. Will the passengers be able to find a way to escape the competition? Will there be any retribution against the orchestrators of this sick crime?

After a tragic accident at a large facility 6000 meters below water killed its workers, the facility was abandoned for three years. After the Japanese company owning it is taken over by a Chinese company, the facility will be opened again. Kadokura Kengo and his colleague Danzaki are sent along with the team reopening the underwater facility. However, right away, an 'accident' grievously injures Danzaki. Kengo is left alone with colleagues he doesn't trust in an eerie underwater environment that may have more to it than meets the eye...

Abara is set in a dystopian world, filled with large structures. The story revolves around creatures known as Gaunas, those who can shape bone like armor and weaponry around themselves by transforming. The transformation begins around the spine and then shapes layered armor.

The story focuses on one such Gauna known as Kudou Denji, though he uses Itou Denji as a fake name early on.

Abara means "ribs" in Japanese.

Volume 2 contains Digimortal
A mercenary in cyber-armor battles a repressive cyborg regime.

From Aerandria Scans:

I suddenly lost my parents. Without a single relative, I must return to my father's birthplace, a village, where I can finish school. But I still cannot recover from the sadness. I am lost in doubts and insecurity. And then, on a mountain road, among the lush greenery, who do I chance to meet..?

From Tokyopop:

Beautiful creatures called 'Alichino' grant any wish to those who find them--but at a price!

A young lady searching for an Alichino wants to bring her brother back to life. She meets Tsugiri, a handsome young man who she thinks is an Alichino. While Tsugiri turns out to be a mere mortal, he does have a mysterious connection with these rare creatures--a connection that brings him and those around him grave danger!

A sort of horror-mystery, Anamorphosis revolves around a group of people invited to a contest wherein they have to stay in a supposedly haunted set for 48 hours after an evil murderous spirit is summoned to produce a recreation of the murder scene.

Over half of the book features this story and the rest is a collection of bizarre shorts designed to make you go
( ﾟдﾟ)！？

From ShoujoMagic:

A collection of short horror stories from the pages of Ciao Magazine.

Story 01 - The Scream of Glass
Story 02 - I Want The Lead Role
Story 03 - Exciting Mysterious Club
Story 04 - I Want To Be With You Forever
Story 05 - Haunted Afternoon
Story 06 - My Place In The World

26 years ago, in a third-year classroom of a middle school, there was a student named Misaki. As an honors student who was also good at sports, the charming girl was popular with her classmates. When she suddenly died, her classmates decided to carry on as if she was still alive until graduation. Then, in the spring of 1998, a boy named Kouichi Sakakibara transfers to that classroom, and he grows suspicious of the fearful atmosphere in that classroom. In particular, there is a beautiful, aloof girl named Misaki Mei who wears an eyepatch and is always alone drawing pictures.

From AQUA Scans:

"In an accident at the meat factory, the heiress was heavily injured. Guiltily, I agreed to her request, but this very same request have let me enter into a wonderful life..."

From ADV:

While trying to bury the body of his mother deep in the woods, high school student Yuri is approached by a strange girl who offers to help him. That is... if he promises to be her "parent killing assistant." Meet Anne Freaks, a bright, attractive teenage girl normal in every way - except that she's on a mission to kill her father, the leader of the dangerous extremist cult: the Kakusei Group.

27 year-old Ayukawa Yuuji has never been much of a man. He's more comfortable sewing than fighting, he faints at the sight of blood, and his fiancee is tougher than he is. He's also a terrible pushover. So when his boss at the medical lab volunteers him for some experimental drug therapy, how can he possibly refuse? All's mediocre for Yuuji: master of the pathetic.

Mediocre, that is, until a juvenile mass murder suspect jumps out from under Yuuji's bed, declaring him his "mate." Before Yuuji has time to argue, the stranger transforms into a 16 foot-tall dinosaur and beheads his roommate...

Yuuji suddenly finds himself the sole target of a lost race that turns into dinosaurs, an extremely scary woman with a Goddess-Complex, the yakuza, a mad scientist and one 17 year-old boy who really, really, really wants to sleep with him.

Series:
1. Aragami no Ichizoku (4 volumes)
2. Daichi no Okite (2 volumes)
3. Genshi Sairai (10 volumes)

27 year-old Ayukawa Yuuji has never been much of a man. He's more comfortable sewing than fighting, he faints at the sight of blood, and his fiancee is tougher than he is. He's also a terrible pushover. So when his boss at the medical lab volunteers him for some experimental drug therapy, how can he possibly refuse? All's mediocre for Yuuji: master of the pathetic.

Mediocre, that is, until a juvenile mass murder suspect jumps out from under Yuuji's bed, declaring him his "mate." Before Yuuji has time to argue, the stranger transforms into a 16 foot-tall dinosaur and beheads his roommate...

Yuuji suddenly finds himself the sole target of a lost race that turns into dinosaurs, an extremely scary woman with a Goddess-Complex, the yakuza, a mad scientist and one 17 year-old boy who really, really, really wants to sleep with him.

Series:
1. Aragami no Ichizoku (4 volumes)
2. Daichi no Okite (2 volumes)
3. Genshi Sairai (10 volumes)