Teppei Arima is a second-year high school student who lost both of his parents in a traffic accident on their way home from a family trip. His grandfather, Isshin Arima, happens to wield the puppet strings in Japan’s vast economy and demands that Teppei becomes his successor as the head of the Arima Group. To prepare for his debut into high society, Teppei enrolls in an elite academy for the scions of the rich and powerful.

Wakaba Chiharu is a fujoshi, but hides it from her friends. She fantasizes about male classmates being intimate and uses them for her manuscripts. But somebody is interfering with her daydreams...

A high school girls' portball (simplified version of basketball) team plays against the boys' team to fight for the right to exist!

Set in feudal Japan, Sorano is often mistaken for a girl, and he is saved one day by Iori from some pushy guys; the two hang out together the following day.

Really short like 4 pages

44 years old and still unmarried, construction worker Kurosawa wants nothing more than a little respect from his co-workers...and some popularity wouldn't hurt either. Unfortunately, Kurosawa's awkwardness and lack of social aptitude causes any attempts he makes to that effect to fail miserably time and again. But one day, his already bad luck takes a sudden turn for the worse.

From Rayns&Lele Scans:

No matter how you look at it, Kamijou is an average guy. On the other hand, his ex-childhood friend, Aikawa Itasu, is a popular and intelligent girl. Believing his childhood friend to be in a whole other world than himself, he starts putting distance between them...
Until one day, Kamijou’s cat, Peace, sneaks off and visits Aikawa. The two of them starts talking again. What's Aikawa's motive for feeding Peace? And... will they end up reconnecting?

Palepoli goes beyond the framework of standard four-panel manga and views its structure in new ways. Actually, Furuya knew nothing of conventional manga styles and methods when he started Palepoli. As a result, he created something that bore little similarity to other manga. Furuya notes that he selects his subject matter and methods with clear and precise intentions.

A portion of Palepoli was featured in Secret Comics Japan.

Quoted from 4dawgz (the scanlator)-
"So there's a magazine called Gelatin where various manga artists are given some coloring crayons and then told to draw whatever they want in full color. The plot for this is about a guy and a girl who go on a mission to retrieve a pair of shorts from an island... aaaaand that's it. All you'll find is a nice slice-of-life story and lovely colored pages."

Sugano Ikkei is a typical teenager at his high school and lives with his older brother Hyakkei who is an editor at a publishing company. Hyakkei is in charge of several artists and writers and his job is to support them in anyway possible. However, he broke his leg and is unable to leave the hospital for a week and he has a very important meeting with a very shy writer named Tokito Aona which has taken months to get a face to face meeting. As they look really alike, he asks Ikkei to dress up as him and go as Hyakkei. The meeting goes well without her knowing the truth, but Ikkei is forced to go to another meeting with Fujimaki Misuzu, an artist moving to Tokyo in order to continue working. To his surprise, both girls, Tokito and Fujimaki, are in the same class as he. Now he has to juggle being Hyakkei as an editor to the two girls as well as be their classmates as Ikkei, and do all this without letting out the secret that he is the same person.

After a four-year absence, Ishida Kotori (QP) returns to the city where even his face instills fear amongst the locals. Trying desperately to move away from his once violent past and live an honest life, former classmate and now high profile gang member, Azuma Ryou, has other plans for QP's future...

QP: Soul of Violence is written by Takahashi Hiroshi and set within the same universe as his other works, Crows and Worst.

4-koma manga

One day, an un-named ordinary high school girl (her name is left to your imagination), meets Cheko, a maid sent forth from a village of maids. Cheko the maid can melt, fly, remove her head and violate physics.

Surrounding the "ordinary high school girl" and her strange little maid are yuki-onna's who hate cold, a cute squid that can speak, moe yankees, tsundere maid assasins, ecchi lesbian teachers, trap yuki-otoko's, gentlemanly yakuza and many more.

She calls herself Sexy Voice. To most of the world, she's just Hayashi Niko, an ordinary schoolgirl - but when time permits, she lives a double life as a hired investigator/spy. To help her, she has recruited the rather unlikely assistant she calls Robo, a geeky lump of a man who doesn't really know why he feels the need to do everything she tells him to. He just does it. Together, the odd team solve a number of cases for Sexy Voice's employer, an aging gangster.

Nanami Sekai gets scammed out of every penny he has, left only with a pair of boxers and a 3,000,000 yen debt. He then meets a girl, Ritori, who offers him a deal that seems too good to be true: she will take care of his debt if he will be her captain and help her with her job.

[Note]
It seems that this manga has been discontinued because the author became incapacitated during serialization and was not able to keep 2 series running.

Sasameki Koto is the story of Murasame Sumika, an intelligent and athletically gifted girl who just happens to be in love with her best friend, Kazama Ushio. Unable to confess her feelings, Sumika can only stay by her side and watch over her. After all, the biggest obstacle to her love is something that she can't change. It has nothing to do with the fact they're both girls; Sumika just isn't Kazama's type!

Kazama is only into cute girls and Sumika's cool personality just doesn't fit the bill. Much to her friend's dismay, Kazama is always eager to share news about her latest crush. With the duo's knack for attracting trouble, it looks like Sumika's trials have only just begun.

Moyoco Anno lifts the veil on life in the Edo period pleasure quarter, Yoshiwara. The story follows Kiyoha, sold into a brothel as a child and forced to work as a maid and her rise to prominence as one of the top-ranking courtesans in Yoshiwara. The allure of the "flower and willow world," as it was called by artists in the day, is underscored by the very real tragedy, heartbreak and difficult lives led by those seemingly glamourous courtesans. Will Kiyoha’s fox-like wiles give her a chance to break free of her gilded cage? Or will her fighting spirit ruin her chances of ever escaping the brothel?

Mizutani Minato, a high school girl, has not fit in at her new school ever since she started attending a different school from her middle school friends. Her shy personality has kept her from making friends and engaging with her classmates. Through an unexpected turn of events, she joins the astronomy club in school, consisting of three students considered to be the weirdest and seen as outcasts in the entire campus. The club consists of Aida Souji, the smartest student in the entire freshman class, Kousaka Ranko, the second most brilliant and ridiculously strong, and Takigawa Youichi. They all have dreams of becoming members of NASA and studying the fascinating universe. The four kids of the astronomy club rename themselves “Soramiyo” a name made by taking the first letter from each of the members' name. Minato slowly learns through the Soramiyo club how to become confident in who she really is and the importance of having great friends.

Shante Lisveriat, an alien, comes to earth in search of a bride, selecting skeptical middle-schooler Konomi.

Maeda Shinshi is a typical 24-year-old white collar worker and he receives an anonymous love letter from a girl. He finds out that the girl in love with him is an elementary school girl named Oyamada Nana, a very quiet, shy and a little confused girl. Shinshi has no idea how to interact with Nana and everytime he tries to make her feel comfortable, it ends up blowing up in his face and he ends up looking like a pervert. Will Nana ever be able to convey her emotion to him and will Shinshi stop doing things that make him get mistaken for a perverted lolicon?

As a boy, Taishi saved a tiny chick (as in an actual bird) that was being bullied by its brothers and sisters. And now it’s grown up into a hot girl who wants to cater to his every whim! Did we mention she lays eggs, too?