An introverted Otaku was summoned to a Fantasy world, and successfully defeated the Demon King there. Just before the ritual to send him back to Japan was complete, the country's Princess dashed into the middle of the spell to be with him.

When they both opened their eyes, they realized they were transported to a Sci-Fi themed world than neither of them recognized. Working together, they must now survive in an unknown world and find some way to get home.

The great sage, Grameos, tired of his current life as a famous mage, decided to reincarnate as a young boy 200 years in the future. Before reincarnating, he places two magic restraint seals on his hands, so that he can hide his enormous magical power after he is reborn. His motto for the next life is "Hide my powers, don't stand out, and be free".

I’ve been reincarnated into a world of strategic gaming where I acquired number 1 Rank!

I thought I would be reincarnated as a warrior in a gaming world that I know of, but I found myself to be a rogue lord who dies in the prologue! And I only have one day left before I die due to another country’s invasion..!

Use all your wits, courage, and gaming knowledge to face your destiny!

It’s a strategic fantasy where you risk your life to turn the tables!

Pocket Monsters stars a Pokémon Trainer named Red and his rude Clefairy. It is chiefly a gag manga, using crude humor and slapstick.
The series diverges somewhat from the Pokémon video game and anime canon: most Pokémon can speak human language and regular animals (like birds and fish) appear alongside Pokémon. Evolution is also significantly different in Pokémon Pocket Monsters: Pokémon can evolve at any time, and they are also able to reverse the evolution.
-Bulbapedia

In a world filled with talking Pokemon, Red and Green compete with each other in a race to gather all the data needed for the new Pokedex! Bumbling Clefairy frustrates Red with its extreme incompetence and silly behaviour... however, sometimes Clefairy's bizarre ideas to work out in the most surprising ways!!
-Chuang Yi

The main character, Hazel (Maron in the original Japanese version), sets off to catch Pokémon after a scientist named Grandpa agrees to make a love potion if she catches Pokémon. Hazel is after the heart of a boy named Almond. Most of the Pokémon in the manga series can speak a human language. The manga's plotline has nothing to do with the original video games. Taken from Wikipedia.

Satou Shiki, a university student, was suddenly stabbed by a slasher only to be reincarnated in Labyrinth City. In this other world, he who has awakened to [Appraisal] and [Healing Magic] does a lot of “things”.

In the second half of the 2nd century, Naru, a warrior from the state of Koryo, was sold as a gladiator-slave to the Roman Empire and waged a desperate struggle for freedom.

From Tokyopop:
After an imprisonment of five days in Heaven, which equals five years on Earth, Soma is sent to the human world to recover the lost sword. Under the supervision of the heavenly princess Aroomee, Soma must deal with the chaos that his deeds have produced.

This manga follows the adventures of a group of mercenaries: the barbarian Mocha (the main character), the rogue Buruman, and the mage Kiliman (Blue Mountain and Killie Mountain, respectively, are famous coffee brands in Japan).

Mocha and her gang belong to a dark mercenary guild. Mocha, being a barbarian, has great physical strength and, of course, she has no brain. Despite her very revealing suit, she is very innocent, pure and naive. The story starts when a light master seeks to hire some mercenaries, and the guild refuses to help him since he has no money with him. So the dark guild master sends Mocha, Buruman, and Kiliman to aid him. It's really not a great start but this is how everything begins.

The author's drawing dramatically improves after volume 5. The plot becomes much more refined as well. It can be considered a typical adventure story. However, this manga goes a little deeper than that.

After volume 10 or so, the plot becomes really profound and deep. Dragons are involved, and whole nations go to war. The scale becomes quite large. Really enjoyable manga.

In a world that always has 16 heros, Sion [Shion] is a hero of darkness and the strongest. But he has been tricked by his own companies. Being sucked power, He was teleported to a far place…

After the great war of the late 1990s as Japan begins construction on a new capital city, earthquakes cause massive destruction and rumors of demons have begun to emerge. The protagonist receives a warning and a demon summoning program.

In the region of Kalos, an old tale spoke of two legendary Pokemon, Xerneas and Yveltal, who were said to appear every 1000 years to clash with each other. The myth became a reality when the two showed up inVaniville Town one day, wrecking havoc to everything in the area.With their homes destroyed, X, a prodigy in battling who went into seclusion after an incident related to to the paparazzi, was forced to go on a journey with his childhood friends: Y, a Sky Trainer in training; Trevor the scholar-to-be; Tierno the dancing expert; and Shauna, who aspired to become a Furfrou Stylist. Under the constant threat of the ominous Team Flare, who was after X's mysterious Mega Ring, the five young trainers must stick together and depend on each other to weather through each challege and seek what they find, including an answer to the mystery of Mega Evolution...

The world’s first action game VRMMO FWO (Fantasy World Online). Our main character chose to become a Summoner. While not so much in particularly willing to go about aggressively capturing monsters or aim to be the strongest player. Just wanting to have an adventure to search for cute monsters and clothes’ material. Without noticing in the flow of one situation after another, he becomes the top ranking Summoner.

From DGM:
WITH LOVE, ANYTHING'S POSSIBLE
A little unicorn named Unico lives with his mistress Psyche, bringing her happiness and good fortune in return for her unconditional love. The goddess Venus, however, grows jealous of Psyche's legions of admirers and flings Unico across time and space! When he awakens, he's facing down mean buffalo in the American West, with no memory of Psyche or his past life.
It's the first of many exciting adventures that will bring Unico face to face with high society in Imperial Russia, characters from fairy tales and Shakespeare, and even an automated factory intent on blotting out the sun.

Midorimaru Matsunoki, the only son of lord Matsunoki Mumeharu, retainer of Hideyoshi Toyotomi, becomes involved in his father's secret plans about construction of a new castle. Soon after encounters a female peasant school teacher, Tae, who becomes his lover. Circumstances even come to affect the beautiful female noble Yayoi, who hates (and loves) him, and his beloved sensei, samurai Fujinosuke Murasaki, the main constructer of the castle, in ways no one would have anticipated...

This is a fast-paced story with overt characterization that reflects on the fairness of love and war.

The manga that made Tezuka famous. It is an action-adventure drama inspired by Robert Louis Stevenson's book.
One day a boy named Pete finds a map of "Treasure Island" that his deceased father left behind. He starts on a voyage to find it together with "Captain," who was a friend of his father. But his ship is attacked by pirates, led by Bowarl, and the two are caught. When a storm hits the pirate ship, the two are thrown into the sea and washed up on the shore of a solitary island in the southern ocean. To their surprise, this island is the one they have been looking for....
The Western-style art and fast-paced storyline attracted much attention, and it became a best seller with 400,000 copies sold, laying the groundwork for the manga craze and its modern style.
The original version of "New Treasure Island" was based on Tezuka Osamu's manuscript, but substantial modifications were made by Sasaki Shichima, who cut nearly 60 pages and also changed some of the lines. When publishing "The Complete Works of Tezuka Osamu," Tezuka Osamu remade it based on his memory to make it closer to his original.

The story takes the place in the world where using the magical powers is natural. Hiasen, the son of Ran, is raised by the powerful wizard, Kasin, who is also a friend of Ran. The story begins with the time when Hiasen asked Kasin to send him to the school for a gift of Melly Day (February 29th, comes in every 4 years).

Hitto Tamaga, an 11-year-old boy, lives in some town in Japan. He is a very unfortunate boy, whose only asset is brightness. He lives only with his father who is a B-daman researcher, but he left home several months ago, and he's been missing since then. He is living alone in a hut built on a relative’s land. Nobody celebrates his 11th birthday...except his cousin Nana who lives in the same land. One day, Hitto receives a present from the lost father, and he is very grad to know that his father remembers his birthday. It is “Crash B-daman” that he longed for. After he puts them together to complete Crash B-daman, he brings it to B-Park, or a battle field of B-daman. A battle there shows him a new way he should go.

There is a message from his father with the present.

“Overcome the difficulties”.

Putting this word in his mind, he beats the enemies one after another with his B-daman. With the encounter of partners and rivals, the mystery of B-daman, a shadow organization, and the reason of the missing of his father gradually come to light. Defeating various obstacles in his way, he’s growing up.

42 year old “shachiku” (company slave) Matsuda Takeshi gets worked to death, as is customary in Japan. His one dying wish is to work for a decent enterprise, not the black company he had been working for. His wish is heard by a god who, for his own amusement, has him reincarnate as a young elf male in another world, with increased affinity for earth magic and ability to command golems. The new golem master sets out on a quest to acquire the Seven Treasures left behind by a legendary mage from 1000 years ago.

I am Owen Pepper, the heir of a Noble family. To begin with, there are two kinds of people in this world. The aristocracy, winners from birth, and the rest of the losers, the cattle. I am a winner, of course. Bwahahaha. Livestock, you can work hard for me today. It is the only thing you lot are good for! I have been reincarnated as a tr*sh aristocrat. My father was a villainous lord. And his son, Owen, has been deeply influenced by his father and has grown up to be a fat, incompetent boy! If this continues, my future is in jeopardy. … But I do not care about that! “I heard that there is magic in this world. If we are going to go to all this trouble, let us try to master magic!” And if you are having fun learning magic, you will soon be able to break the stigma!
(taken of NovelUpdates)