Watanabe Yuuichi, also known as Pen-chan, loves mahjong. It's just too bad that he's not very good at it. Follow Pen-chan's wins and losses (mostly losses) in a series of short tales about his friends, family, co-workers, and local yakuza until the final conclusion where Pen-chan makes the biggest gamble of his life...

Tenma is a Middle Schooler who loves playing Mahjong. He doesn't know exactly why, but the freedom it brings him fills his chest with pride. One day, his friends run into some trouble with University Students from Kantou, and it's up to Tenma to save the day!

It also has 1 Volume (Collector's Edition) called "Tetsu to Tenma" (Including "Atsuize! Tenma" and "Burai na kaze Tetsu" in a single volume).

Goryo Daisuke is still unsure about which club to join. When he meets the three girl members of Mysterious Research Club while looking for the school's warehouse, he gets hypnotized to sign the registration form. Suzu who is obsessed with scary curses, Chiaki who only relies on her monstrous strength to perform dangerous magic tricks, and Kotone who can control people by hypnosis.

From Easy Going Scans:

Sui and Sou are a pair of twins who are starting high school. Though raised by occultist parents, they were supposed to have a very normal high school life. However, once they arrived at campus they not only encountered werewolves but also vampires and even sorcerers! As more strange people appear one by one, will the twins' secret be uncovered?

One day middle school student Nishiki, who lives in the countryside, meets high school student Atsumori, who came to visit from Tokyo. When talking with the cool Atsumori, she starts noticing her desire to leave the countryside for Tokyo. But the way to Tokyo is unexpectedly through a marriage proposal?!?

From Wikipedia:

The story is about Kozue Ayuhara, the new girl who transferred to Fujimi College, who tried out for the school volleyball team. Her friendship with Midori would develop, and her talents would impress coach Honga more and more each day. Though she showcased extraordinary volleyball skills, she would make enemies with Yoshimura, the star of the current team. Kozue would discover that being at the top would bring stress, incompatibilities and other dilemmas into her life. Her high expectations of becoming the best volleyball player in the school, Japan and eventually the world, would set the tone for the drama to follow.

In a world entirely ruled by giants, the human race, which has turned into their food, has surrounded its residential zones with immense walls, which both prevent their freedom outside the walls and protect them from incursions. However, as a result of the appearance of supergiants who cross the wall, a desperate struggle begins and the young heroes, who have lost their parents, fight the giant as a training corps, with a view to regaining their freedom.

Note: Won the Kodansha Manga Award in the shōnen category in 2011, was nominated for the 4th annual Manga Taishō award and also for the the 16th and 18th annual Tezuka Osamu Cultural Prize.

Eren and Mikasa enter a new school-- Titan Junior High! However, Eren's hated Titans for years-- can he get along with his new (harmless?) classmates? Featuring all of the characters from the main series as you've never seen them before, this series is sure to delight fans of Attack on Titan with a human vs. Titan volleyball match, a Titan rock band, and much more!

Harutaka Kato, a 1st year student in Kakegawa high school with the extraordinary ability to jump. After seeing his ability, Maiko the volleyball club manager kept urging him to join the team. Finally, Harutaka was persuaded to enter the club. However, the volleyball club had another star, Yuta Kaneko! Harutaka was upset and tried to show off but all of his smash was blocked by Yuta!! So, what will Harutaka do!?

From Easy Going Scans:

Leesu came from a poor family but he didn't mind at all not having any money or status. Being the school's strongest fighter made him feel as if he was on top of the world in his eyes. But alas, a car accident made him lose what was most precious to him; His ability to fight! Craving for his past glorious days he turns to fencing with the hope to regain what he once had?

From WoC Scans:

It's a short story about the mangaka's many cats. They're so furry and cute!

Attemo Nakutemo Neko no Shippo literally means, "it's a cat's tail whether we meet or not" --it's actually a figure of speech meaning "it doesn't really matter if we meet or not" --but in this case, it's a pun because the manga really is about cats.

Jinta, who has never returned in a traffic accident, meets the goddess, Rifua, in heaven.
Jinta was supposed to reach Heaven under the guidance of Rifua,
Reincarnated in a different world from a strange thing.
Immediately after reincarnating, the abnormal status of Jinta was discovered.
Originally the maximum value of luck should be "99", but the value of Jinta is "999999"...!?

Ming is a Year 5 primary school student who had a dull and meaningless school life in the worst class of the worst school in a declining heavy industry city. However one day his deskmate Hua became the class president and declared herself "Empress". The class now goes on a journey to fight against the old order made by adults.

Ever dream of being in a rock band? Ever dream of being in a GENIUS rock band? Could there be such a thing? For Chul, Dal Bong, Mickey, and Rae-young, it’s not a matter of if, but of when. These four deviant misfits of society find themselves stalked, caught, and coerced into forming the greatest boy band of the century. It doesn’t hurt that they have talent, looks, and personality. A female detective, an heiress, a Betsy Johnson-inspired wardrobe, an evil dude, a cute evil dude, and other casts and characters all come together in this brilliant high jinks story of rock ’n roll, friends, and yes, love, that will make you wish you could have been there for the Audition.

Excerpt:

I was worrying sick because of you, so how are you going to repay me?

Ah, en? Repay you?
.........

What's wrong, didn't you say you’d let me do anything I want? Now you want to go back on your words?

Don't always show that kind of expression, it looks like I am the one that's bullying you.

Aura is a certified buff spell caster from Planet Leviathan that came to earth by a portal accident. She attends school on earth as a way of adapting, and never fails to find friends, old alien frenemies, and troubles with her buff spells. Official English Translation

A girl with a strange mother who brings home a new father and stepbrother. She loves photography, and her new stepfather is a photographer. They begin living together and have to overcome many difficulties.

The world under attack by monsters that are pouring from the 'fracture'. And the 'hunters' who hunt those monsters are the most coveted job in the world currently. One day, Oh Yunsung who works his hardest from day to day as a worker in a meat restaurant awakens an ability to automatically hunt monsters with perfect techniques and physical prowess like in MMORPG when he presses a button 'Auto Hunting' that appears in front of him...!

When I regained consciousness, I found myself in an otome game. I would quickly head towards destruction. It made no difference whether it was a good ending or a bad ending. I became the character known as, “Mariabell Tempest,” the daughter of a pedigree family. Despite possessing an unrivaled level of beauty, I had the worst personality, that of a villainess.

Nevertheless, I was conscious, but was unable to make any actions as I was completely in auto-mode. In the first playthrough, I was extremely flustered; on the second playthrough, I was despairing; by the third round, I had already given up. And now, the fifth round has already ended. For the sixth round, for some reason I had become a young girl and regained the ability to move and talk. Eh, what the heck is this?

The human race is becoming more and more dependent on increasingly complex technology and machines; machines that inevitably break down. According to those lucky people who work at ATMT, the best job in the world is to be one of those special people who exists between the human world and the cyber world as "therapists", inserting their consciences into the broken machines via a proprietary interface to conduct the repairs. Such a job is not without immense risk and can result in a person being trapped in the device as an annoying, pitiful bug. Amongst the therapists, there exists a chosen few who have additional power and capabilities and who face the greatest risks and dangers - the Automata.

- Cave Scanlations

Official English Version - also Season 2 & 3
Original webcomic