The protagonist is your average, everyday, Korean school student. That is, if not for his obsession that aliens live on Earth disguised as humans. Much to his surprise, he was right, the aliens play a game called "Avatar" where they take human form and live human lives. And because of a glitch he caused in their system, now his very life could be at risk. Now he needs the protection of an Admin of the "Avatar game" or else he could very well die!

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.

After dating a player who had another girlfriend, Rina decides to become a player also and immediately finds someone willing to be her lifelong toy.

Minori is the manager of her high school's baseball club, which has been defunct up until five years ago. Even now, it's a little rough, since there currently are no seniors in the club at all! None of the second year players know why the club closed so many years ago, or about the baseball history all their fathers share...

From Reverein Scanlations: A series of short stories featuring two characters with the same name, Asuka Koji and Takaki Asuka. They both have super powers and share a common love: SAKE! This really has no real plot but it provides a lot of entertainment and random characters from her other works also appear.

From Ryuusei no Mafia: Minnie’s the only human living on an alien planet and because of that she’s rejected by almost all the other inhabitants. Then one day something falls outside of her house and it happens to be... a human prince?!

A new teacher finds himself a newly appointed position as a teacher at an all girls school... on an island... in the sky! How will he make do in his new surroundings? Or the residents of this island who seem like they came from another world? And what's more, how will he fare at being a teacher?

Vampires exist. It is the duty of Hellsing, an organization sponsored by the British government, to hide that frightening fact and protect the blissfully unaware populace. Along with its own personal army, Hellsing also has a few secret weapons. Alucard, an incredibly powerful vampire, has been controlled by Hellsing for years. Although he dislikes being a servant to the Hellsing family, he certainly enjoys his job as Hellsing’s vampire exterminator. Seras is a fledgling vampire and a former police woman. Although reluctant to embrace her new self, she is still a valuable member of the organization. Integra Hellsing, the current leader, is usually fully capable of fulfilling her duty, but lately, vampire activity has been on the rise. Unfortunately, the cause is more alarming than anything she could have imagined. A group long thought dead has been plotting in secret since their apparent destruction over 50 years ago. Plotting to plunge England, and perhaps the entire world, into war.

From An Endless Story: For normal people, about one unfortunate event occurs in a 1 day period. But for some reason, it's different for Rinko. Unfortunate things seem to pile up one after another. All Rinko wishes for is to find some happiness in her life. With the upcoming New Year's celebration and a date w/ her best friend, Tatsuyuki, will her hopes and dreams be fulfilled?

From Intercross: Makoto Hourai is given to Alice Kamiya as an "offering" because of a long-established contract between the two families. He is there in order to assist Alice, who is actually a vampire. As an offering, Makoto is supposed to give Alice his blood, however, he is anemic. How does Alice manage to drink blood, if Makoto can't provide for her? How does Makoto feel about all this?

From Ochibichan: Miya, Amatsu and Zen have been close friends ever since their childhood. One day, Miya falls in love with a cool high school student, Toujou-kun, so she decides to become his girlfriend. However, Amatsu secretly likes Miya. So, he uses all kinds of ways to interfere with her! Moreover, the three of them have a very huge secret!!

A short prequel to Shounan Jun'ai Gumi and pre-prequel to GTO about how Onizuka Eikichi and Danma Ryuuji meet. Pantyshots and gratuitous asskicking galore. This manga was added as an add-in to Shounan Jun'ai Gumi and later rereleased separately. Some time later GTO came out and the two prequels became more famous.

Hojo wins three wishes from a ticket and makes some choices that affect his senpai in odd ways...

Travelling salespeople visit a small, remote town. However, neither the town, it's inhabitants, nor the salespeople are what anybody would consider "normal". A supernatural crackpot comedy.

A oneshot that appeared in Comic Flapper 2015-02.

From Garo 1982-07.

Ryosuke returns back to his birthplace to help run his family's vineyard after his father gets hospitalized. He has sour memories of his hometown after being shut down by the girl next door, who he admired from day one. That's the whole reason why he's never returned after moving to Tokyo, to attend College, 3 years ago. Despite his reluctant return, Ryosuke happens to be quite popular with the ladies. His sexual endeavors start off with a fling with a former high school classmate, a charming girl working at his parent's vineyard, and a sexy nurse. He even manages to allure the girl next door who he has been dreaming of his whole life but...

From Chibi Manga: Please, teach me about things we can't do ! #1. Ijiwaru na oni Kyoushi...a pretentious and cruel teacher give her private lessons after school?! #2. Geki Kawa Kyoushi…a morose girl with glasses and a handsome teacher = don't tell me it'll have some alchemy between those two?! #3. Kiken na Hokeni …A kind and gentleman teacher is in fact not what he seems to be...!! #4. Onna Kyoushi no Ikenai Koi…Though she's dreaming about an adult and handsome man, she'll become close to a high school boy...?!

Set in the Daiouyama Prefecture High School, a school with over 3000 students. The Student Council Empress decides that small clubs are a blight on the schools resources, and that they should be forcibly merged into one club. Which of course throws four very different clubs and girls with different interests into the same room…

Takaya and Yurina are back in this sequel to dive into their history. Back in kindergarten, Takaya had made fun of Yurina, and now that she's forgiven him in the present, what other things from the past will come to haunt her? Will they be able to resolve all their problems and go back to their peaceful lives...?!

From batoto.net Fujii Kana just broke up with her boyfriend, when her older sister Mizuho calls her to ask for her hospitality for her and... her girlfriend. How will Kana, who hadn't ever imagined her sister to be a lesbian, cope with this cohabitation?

High schoolers Rin and Kyo are childhood friends from kindergarten. They're so close that there's virtually nothing they don't know about each other. Rin, who had been pining for Takahashi-kun, his father's lover, for many years, finally gave up and wished for his father and Takahashi's happiness. After his broken heart was comforted by Kyo, Rin was finally able to stand up again, but then suddenly, he was confessed to by Kyo...?!

Updating

From Entropy: This is a set of one-shot stories of working people drawn from the viewpoint of Matsukata Hiroko, who is a 28-year-old single woman and is an editor of Weekly Magazine, JIDAI. She’s often at odds with Tanaka Kunio, a novice editor. Her work already stresses her out and he’s unapologetic about his own mistakes! Everyone refers to Hiroko as a masculine woman for how seriously she takes her work. She smokes too much, works too much, and never has sex. However, when it’s time to get a story done, she switches into “Working Man” mode where her testosterone in her blood increases, she works three times her normal speed, and all thoughts of life’s necessities disappear.