A Japanese police officer named Kyo Kugayama and Kyo Hoshina, a 12-year old genius with an IQ of 250, embark on a quest to investigate a person known as the Professor. Nothing is known about him, except he is said to be a genius like Hoshina and said to be linked to multiple bombing attacks in Japan when Hoshina was recalled from the US to assist the National Police Agency in their investigation of the bombing cases.

Jin Ah enters the mirrored land and is unable to leave. An adventure awaits her as she attempts to escape from this new world.

From Tokyopop:
Three hundred years ago the Dark Magician Deshwitat Lived Rudbich, a vampire, was sealed in limbo by the Light Magician Kalutika. Resurrected in the present day, Deshwitat has vowed to destroy Kalutika, and now, with the help of a team of spiritual warriors, seeks the means to use Light Magic to achieve his ends.

Motoba Hitachi has lived a boring high school life, until his kouhai invited him to a real-life simulation event of Incubate Castle, an online game they both played. But, what seemed like a harmless replication of the game turned out to be as real as it could get. Now, Hitachi must find allies to get out and survive this reality of a game.

From Viz: Yomiko Readman's love for literature goes far beyond any run-of-the-mill bookworm's! In fact, she has a supernatural ability to manipulate paper in the most amazing ways. From turning a tiny scrap into a lethal throwing dagger to making a single sheet hard enough to block bullets, she's only limited by her imagination. She uses her phenomenal power to seek out legendary books containing secret information that, in the wrong hands, could be dangerous. Backed by a Special Operations Division in England, Yomiko has her hands full battling evildoers, saving the world, and trying to find time to curl up with a good book.

From CMX:
Sakuya and Wakyo are reincarnated and reunited only to discover that Bishu-sama - their master and mentor from a past existence - is in their midst and in grave danger from vengeful demons! Still unsure of their own powers and the nature of their cunning and elusive enemy, they must race against time to rescue Bishu from the dark forces that roil within his reincarnated form.

In a world similar to that of Scheherezade's tales, a mysterious young boy named Aladdin drifts from place to place with his djinn Ugo. Ugo lives inside a golden recorder, and Aladdin is on the hunt for his true container "The Djinn's Metal Vessel".
One day he encounters Alibaba, a poor lad determined to enter one of the mysterious Dungeons that popped up a decade ago in order to make his fortune. Thus the the two begin their adventure in a Persia that never was.

Oneshot that led to the series One Piece.

*Note: There are actually 3 versions of Romance Dawn that were written: This one was written first, then the one featured in Wanted!, and then the final version that is officially part of One Piece.

From manga-koekje:
Imagine a world full of flying dragons, talking mushrooms, burning forests, supernatural bisons and many more strange creatures... Well, Mondo, Rokuna, and Dr. Hiiragi go on some crazy adventures taking on lions and crazy monsters in hopes of creating a passageway between worlds so humans and monsters can live together.

A famous grim reaper without any fail.
Westernburg city's best hunter, Roi, known as 'Roar Scyther' for his trademark gun by the same name, goes on another mission for money!

Witnessing the death of his parents at a very young age, the main character lives in solitary confinement in a forest while trying to hide from monsters. One day, a creature comes claiming that he's a threat and therefore must be killed. Though bewildered and scared, the main character saves the creature from death. It decides to postpone the killing and leaves without any further revelation of the truth behind the statement.

Tatsumiyajima is the central island in the middle of a small cluster of islands, in a sleepy backwater of the Japanese isles. Not much happens there, and the island's young people go to school knowing that their lives are likely to remain peaceful and undisturbed. Or so they have been taught... but the truth is different. The fate of mankind is on the line, and Tatsumiyajima is the last line of defense against a hostile and incomprehensible enemy. At the center of it all, fighting for Humanity's continued existence, is the giant robot Fafner, the dragon that guards this final treasure of mankind.

Revery Earth presents you with three meanings, one per each volume. Eric is on a journey to revenge his brother's death, Jurd. He saves a prince who identified himself as Sion. Giving Eric an awkward reason, Sion helps Eric on his journey.Eric and Sion come across a town where reports of a strange light in a forest nearby. Eric and Sion seek out the light and ended up finding out the lights were fairies. One of the fairies, Rem, joins Eric and Sion.

[Taken from JanimeS]

Two brothers wearing bunnysuits hop on a phallic train and travel to a mysterious underwater brothel.

From etc:

Ryo thinks she is a normal girl living a normal high school life in modern day Tokyo. But is she? On a school trip, a mysterious man attacks her and claims that he is Benkei, the legendary warrior monk who collected 999 of his opponents' swords in battle during the Heinan era. And he also claims that she is Ushiwakamura, the 1000th opponent, that according to folklore, beat Benkei and became his master. But...Ushiwakamura was a man! And Benkei and Ushiwakamura existed in 13th century feudal Japan!

Another dead body has washed ashore, and the adorably cute, pony-tailed doshin Aki wants to find the murderer. Instead he meets mysterious Kuga who seems to know more than he is willing or can say, but what else needs to be said as Kuga captures Aki's lips? Are Kuga's feelings real or is he trying to distract Aki from his investigation?

Kotoko and Natsuki are shoujo detectives, who are looking for the Three Carving, which holds magical powers. A third girl joins them, and they must solve the mystery and fight the evil, to protect and save the people. [From Owl Scans]

From Viz:

Momoka Sendou (nicknamed 'Dragon Girl') and Ryuga Kou are childhood friends. Momoka is a martial artist, and Ryuga is a Chinese magic master who banishes demons. In order to increase his power, Ryuga calls on the spirit of a dragon to possess him, but the spirit enters Momoka instead. Now the two must unite forces and fight demons together!

In the castle, a poor boy, Biskyu Cris, tries to steal a medicinal herb which can extend the life span of the Castral people who only live for 25 years. Biskyu is saved by a tall beautiful, person completely covered by a long coat.

After a lengthy period of sword training, Biskyu returns to the castle to become a knight and guard the person who originally saved him. Biskyu believed the person was a woman and wanted to sacrifice his life for her. However, his savior was a *king* of Castral, Erudora, who's 700 years old. (Erudora contracted with the Gyokuto people who have magical powers to cure any diseases. In return for his blood, Erudora received eternal life and awful blue blood which grows the medicinal herb.)

Biskyu has the opportunity to become a knight Erudora's daughter, but instead falls in love with Erudora again. Biskyu, learning of the conspiracy by the Minister of Justice to try and kill Erudora, escapes with Erudora to release him from his accursed fate...