Onee-san no Jijou (Sister's Situation) is about a 16-year old high schooler named Tsukiko. She has a crush on a guy in her class, who is also a popular rookie soccer player named Kou. The thing is, her mom just got remarried... to Kou's father, making Tsukiko and Kou step-siblings.

From Aerandria Scans: My mama is in heaven, but...I have my big sister!! Hinako is a high school students who has a lot of things that she wants to do, but for her cute little sister, she will become a mother!

Taken from VIZ:

Kosaku Hatanaka is the first pro boxer ever produced by Mukaida's Gym. He's also the bane of his coach's existence. Although he's constantly waging war against his appetite, Kosaku never met a meal he didn't like! Naturally, this plays havoc with his weight class. Junior bantamweight, bantamweight, junior featherweight... every time he moves up a class, his coach's hopes plummet. Isn't gluttony a sin?

Sister Angela is a young novice nun who's dedicated, passionate, and convinced that we should give peace a chance. Although she refuses to acknowledge it, it's obvious that Kosaku comes to St. Mary's for more than confession! He comes to see the smile of the beautiful sister, of course! Can her faith redeem the gluttonous appetite of the tempted lamb astride the scale?

Story 1. Boy Next Door
Takeshi is straight until he sees Kazuya lying naked on his friend's couch. After their intimate encounter, can they find a way to make a relationship work and manage to survive on their unusual part time job?

Story 2. One Heart
A story about a part-time, student worker and his ex-salaryman boss. When his boss's company is in danger of going bankrupt, how will the part-timer convince his ex-salaryman to take a loan from him?

Story 3. Otoshimono
An odd encounter between two strangers results in tales of violence of questionable validity--and of course sex. But is this just a one night stand?

Story 4. Long Way Home
Katou has money problems, loans and he hasn’t paid his rent for 5 months now. When his realtor Yui suggest that, if Katou does a job for him, he will give him 3 more weeks to pay the rent (before kicking him out or worse), Katou happily agrees… (Yui appears also in Night Walk)

1-2) On the Quiet
On a cold winter day, when Ikewaki Kou, a college student, forgot his key and couldn't enter his apartment, he was invited into his neighbour, Shiraishi Hiroya's room. But the room was so dirty that there wasn't even space for him to put his foot down, and Kou was really shocked by this gap from his neighbour's orderly image. Even so, Kou remembers the steady palpitation of his heart as he conversed with the bashful and unaffected Shiraishi. Things got heated when Kou realised that Shiraishi might like his brother instead.

3-4) Tangerine Report
Nakatani is a nice guy... to everyone else in school. For some reason, he seems to hate Ikeuchi. What could be the reason? Ikeuchi finds himself drawn to Nakatani after seeing the sunlight turn his hair a beautiful color, along with an arousing desire to touch him.
"I always smile gently, because I'm scared of being shunned." Part two is told from Nakatani's point of view.

5-6) Unreasonable Baby
Sugimoto, from Tangerine Report, is back with his own story this time. He took his friends' gay relationship very well... but why? It turns out, he's had some experience himself... with his senpai Kotegawa.
Second part told from Kotegawa's point of view.

1) Ritsujoukan Crisis - Caught in the middle! Tagosaku Yamakawa just moved to the big city to be a housekeeper at an all boys boarding school, even though he's only sixteen. However, part of his job is to control the unruly class G. This includes an Italian exchange student obsessed with figurines, a 30-year-old guy with a gun(?), Kazamatsuri, who thinks of Tagosaku as his pet gerbil, and various other scary guys. Will Tagosaku survive? 3) After 15 - Relationship between the teacher and old army guy. 4-6) Gaku Ran (shojo story).

N/A

THE ITALIAN PLAYBOY'S SECRET SON

from fictiondb:
Conveniently wed!

Cesar Villon de Falcon: the world's finest racing-car driver and Monaco's most notorious playboy. But a terrifying crash has left him fighting for his life.

Sarah Priestley: the enchanting woman at his bedside, who has a secret she hopes will help revive him--Cesar has a son!

The little boy who has his daddy's eyes gives Cesar a new lease on life. But it is his convenient marriage to Sarah that has the potential to make this courageous man whole again....

"What's going on? I just don't get it. Ever since I met Hashimoto, my heart's been filled with emotions I've never felt before..."

Since meeting Hashimoto, whose personality is the complete opposite of his, which is flippant and cold to others, high school student, Makino, can no longer hide the changes within his heart.

Oshaberi na Jikanwari is based on Mizusawa Megumi-sensei's own love story. It is the story of how she had a crush on a boy since primary school and the events that took place while she goes from primary school through junior high to senior high.
(From Esthétique)

Includes a side story about one of the main character's friend, Satsuki Goto, and several oneshots by the author:

The Message
Akari has been keeping a secret from her friend and crush, Wataru. In the spring of 10th grade, she found a tape of Wataru confessing his love to Yayoi, and even after knowing Yayoi had feelings for Wataru, she still hid the tape! Now, two years later, the Akari and Wataru pleasantly bump into Yayoi again...

Landscape of the Second Year
Soko, a second year college art student, is still secretly struggling with her past breakup, but with the help of Kando, overcomes it.

Ever feel like you just want to sit in a corner and just curl into a little ball? Or when your world seems to be too crowded, you just fight against your fate? Yuuji Tsukamoto can't do either. He’s the son of a very successful business man and is as suave as Takehito Koyasu’s voice when he talks. But one thing he wants is out of his reach: Takuya Matsui. Will his constant watching over this boy lead to both of their destructions? The obsession begins…

From Attractive Fascinante: 1-2) The Mermaid of A Back Alley The club manager, Kagami, saved a pretty guy, Ran, in a middle of a rainy night. Kagami couldn’t stop himself from devouring the beautiful Ran after taking him back. Ran accepted Kagami and also learned whatever Kagami taught him. But where does Ran come from and how is he related to Kagami? Several oneshots follow. 3) Execute In The Night 4) Assistant Professor Ogura's Love Lecture 5) Night Joker 6) Small Resistance To A White Robe 7) Small Resistance To A White Robe ~ Preview

From Fantasyshrine:

My senpai is super-hot, super-popular, and a super-model. Rumor has it that he always invites his target to the library and ravishes that person right there and then…
Which is why I was totally shocked when he suddenly asked me to join him at the library!?— I’m ecstatic!!!
My body is already burning in anticipation—!

Ch. 1 - Our Plan of Copulation
Ch. 2 - Underwear Thief
Ch. 3 - Apartment's Peephole
Ch. 4 - Strip Tease in the Bath
Ch. 5 - Even Though I'm Older...
Ch. 6 - Even if It's Painful
Ch. 7 - When The Cherry Blossoms Bloom
Ch. 8 - Extra for ch3, title: Hole

From Chibi Manga:

The everyday misfortunes that occur are from her prayers to God. She believed that her parents and the sister that she loved so much died because of her unhappy predisposition. She can’t even make friends, but all she does is just continue to pray everyday…
And then one day, she met Koini who is invincible at fighting and Kinzou who is invincible against love and was told “we will protect you”!?
This is a high tension love comedy.

From Nagareboshi Manga:

・Oresama Ouji
Sawa hates Judo. She was once really good at it, but boys always rejected her because she was so strong. Now she's entering high school and the gorgeous captain of the Judo club has selected Sawa (against her will) to be the club manager! He also claims he knows her from the past... How will Sawa deal with managing the sport she hates most, especially since the captain seems to like her?!

・Koishiteru...

・Koiseyo!! Onna no Ko

1-4. I Am the Champion of Love
Top model Asagi has a tooth ache, but after meeting the single dentist, Yui, it's not just his tooth that aches. But Yui is not interested in a relationship and just wants Asagi to go away. Can Asagi convince Yui that there is more to life than work? Can dental chairs really be used that way?

5. Holding onto Love
Hiroyuki is always being compared to his older brother, Kouichi, and he always loses. Even Hiroyuki's crush, Kei sempai confesses to Kouichi. Will Hiroyuki fight for the one he loves?

6. Only You Can
When his younger cousin Touya moves in, bored Masayasu decides to have some fun with the strait-laced student. But what starts as a joke becomes much more serious.

From Exiled Rebels Scans:

1-4 + Extra)
In the middle of a turf war between the raccoons and the foxes are trapped the rabbits. The rabbits receive a proposal from the divine fox spirits saying that they will protect them if they hand over a beautiful bride. However, since there are no girls of a marriageable age, Rikka (the rabbits’s head son) decides to go talk to the divine foxes. What he did not expect was that the head son of the foxes, Shirou, would fall in love at first sight with him. How will these two opposites get along? Can a fox really love a rabbit?

5-6)
A salaryman goes through too much stress in work and ends up addicted to sex. Since women can be problematic, he chooses to go to a gay sex agency. There he meets Haruki, who easily sneaks into his everyday thoughts.

1) Otonage
Shunji and Yasushi have been cohabiting for a month and Yasushi is head over heels for Shunji, an excellent home-maker in and out of the bedroom, despite his grumpy disposition. (Continuing story of a tempestuous relationship between Nakano Shunji and Yasushi Mejiro whose story begins in Kawaige.)

2) Otonage 2 (Initial Stage)
Yasushi's ex-lover/cousin reappears and tries to get in between Yasushi and Shunji, causing Shunji uncertainty over their relationship. Other the other hand, Yasushi is worried that Shunji might still be holding a torch for Kousei and it is driving him crazy.

3) Otonage 2 (Final Stage)
Kanako's pregnancy is causing a big chasm in their relationship.

4) Otonage 3
Their tempestuous relationship has finally calmed down but Yasushi is down with German Measles! While Shunji has to work without Yasushi, he meets the son of his ex-probabtion officer.

Otona to Kodomo no Kyoukaisen (roughly means A Man-Child's Boundary Line)

From Peccatore Sanctuary:

Tohru is confused and in deep trouble. After the 'thing' with Takafumi - a senior high student, Tohru can't get him out of his head. Tohru swore that he will wait until Takumi is legally an adult he will not do 'H things' (perverted things) with him. However, both are finding it hard to keep their urges under control... this is when the line between boy and man becomes conveniently blurred...