Suwa Daisuke is an ordinary, but popular, high school student. One of his classmates, Aikawa Hinako, is somewhat fearful of men and because she ran away from just his attempt to touch her hair, he states to one of his buddies, that she is the only one he wouldn't date, unaware all of the people in his classroom could hear them, including Hinako.
Daisuke's attitude changes after he unintentionally hears a shocking truth that she confesses in an abandoned church. His former annoyance turns to compassion and concern. Hinako is unaware that he knows her 'little' secret. Believing him to have no romantic interest, she becomes more relaxed and comfortable in his company. Their relationship faces a lot of obstacles, including jealous classmates.

There's a guy that's been on my mind - Michinaga. One day he told me, "Taka, I have a crush on the teacher." But it hurts me to see his pained expression. Forget about that teacher. Forget about love that'll never bloom. Choose me instead... Taka and Michi, Michi and the teacher, the teacher and Taka's older brother... Where will all their one-sided feelings take them?

From StarryHeaven:

A sweet shoujo story about a high-school girl named Rina who falls in love with Hiro, the guitarist of a band and member of the archery club. They have to deal with many obstacles along the way, especially Rina’s poor health condition.

from hazukashiikedo.wordpress:

Bikkuri suru hodo Doji na Koi
Nao and Tom have been friends since childhood, Nao being the caretaker and Tom being the clumsy airhead. Their high school lives have been fairly uneventful - that is, until Tom suddenly confesses to Nao one night. Nao points out the obvious: “But we’re both boys…?”

Bitansan Danshi
The second story deals with two college students who’re doing a room share. Shimizu Mikio is in his second year of college, and has started rooming with the fluffy, energetic Sawamura Souta. But the more they’re together, the more Miki starts to notice something: Souta seems to like him.

1-3) Bijin Kakumei
During sixth grade Yuki made a love confession to Shin, an extremely beautiful boy. She was extremely shocked when he started teasing her and called her fat and ugly!!
Three years later, Yuki has become beautiful by putting in great effort everyday because she wanted to get back at Shin. She transformed into a very beautiful girl!
She was accepted into the same high school as him to plot her revenge, but her childhood friend Migiwa who knows everything about Yuki's past is attending the same high school!?

4) Gothic Boyfriend (ゴシック彼氏)
Narusaki-Senpai is a famous and widely sold horror novelist, while Himeno loves to write childrens' love stories. She expresses her opinion on her Senpai's writing, but right as she says so, she knocks right into him! Narusaki takes offense to her opinion, and kidnaps her from her sanctuary of cute to his dungeon of horror!

5) Tough Girl's First Love (暴れん坊少女 First Love)
Izumi is considered the "Deity of Girls" (or protector) in her school, but there are sometimes limitations to what one person can do by herself. Kaidou-Senpai steps in, causing her to develop a crush over him.

Mikoto Hiiragi isn't any normal teenage boy. His blood has the special ability to give life to anything, from humans to plants. This makes him very valuable, as those with the special blood types like his are coming to take it away for good!

From Shinnen:
Hibiki and Tomoe Kazema are two sisters attending an ordinary high school, but unbeknown to their teachers and fellow students, they are members of a hidden group of ninjas. Their mission is to use their special powers to exterminate the akuma that are plaguing the world. This is made difficult by the fact that their enemies can possess corrupted humans who eventually turn into new akuma.
Despite being faced with an ever growing army, the two are determined to prevail as "The two flowers that will slice through the darkness." The only question that remains is will they succeed against such overwhelming odds?

From Which Scanlations: Ever since Fune Momohara was told that she was just like a "guy friend" by the boy she liked, she's been bent on becoming the ideal girl. But when she meets the perfect guy who turns out to be more than a little pretentious, she realizes that it can be difficult to keep up appearances!

This dark and intense drama is set in a boy's high school where Kujo becomes the official leader of a gang. Kujo must constantly defend his position by playing a dangerous rooftop game with the other boys vying for his position. This manga has also been made into a film which has shown in various festivals throughout the world. Taiyo Matsumoto made his manga debut in 1986 in the anthology Afternoon, with the short story Straight. His credits include boxing serial Zero, the domestic drama Hanao, the sports manga Ping Pong, the beautiful and violent, Black and White, and the Moebius inspired, No. 5. Black and White and No. 5 were both published by VIZ and scanned by Jinchi who is loved by all US based manga publishers.

Almost two years have passed since Ryousuke made his wish to become a beautiful girl. Although he continuously and faithfully tended the plant that was supposed to make this seemingly impossible transformation a reality, the miracle has yet to happen! To what lengths will Ryousuke go in order to make Gunma fall in love with him? Is it possible that Gunma might actually return Ryousuke’s feelings…!?

From Taciturnity Scans:

Second-year middle school student Ayumu Kurihara changes classes and is seated next to the beautiful but strange Misuzu Tsukishima who dislikes boys. Misuzu can't get close to other people, but after being moved by Ayumu's sweet, honest personality she begins to open up to her little by little. Ayumu too is captivated by the awkwardly delicate Misuzu and the two of them become close.

V.3 (a.k.a. Second Season)
It's Shimizu Kanako's first day at an all-girls high school, and she's a little overwhelmed. Hoping to make new friends, she bumps into the odd and distant Kamei Ao, as well as her first three new friends: Aki, Rikako and Haruna. Of course, not all can be so sweet in the world of girls.

Kayako Kirishima is almost ready to go off to college but is lonely and unsure of her future. Masami Endo is a girl who has been ostracized and made a social outcast for having an abortion. The two girls meet each other in class one day and become good friends. Gradually Kirishima falls in love with Endo and the relationship becomes more personal.

A virus deal clinched in Russia on the Christmas eve. Purpose: unknown. Two clues: a mysterious lady "Maya," who is one of the gangsters, and "Bloody Monday," the keyword for the project.

Then an incident happened in far-distant city of Tokyo. Fujimaru Takagi, a second year student at Mishiro Gakuin high school, is commissioned to find out the truth by the Public Security Intelligence Agency, for his great ability as a super hacker. Now, Maya approaches Fujimaru as his high school teacher...

Kisaragi Saya is a happy, small-town schoolgirl who spends peaceful days with her friends. She mostly hangs out with her friend Yuka, the twins Nono and Nene, and the class rep, who seems to have a crush on her. Saya is also intrigued with a mysterious loner named Tokizane, who always comes to school late. She lives at home with her widowed father, and often eats at the neighboring cafe 'Guimauve,' which is run by the excellent chef and family friend Fumito. Her life may seem very tranquil and happy from the outside, but Saya also secretly wields a mystical sword to defend the town from the 'Old Ones,' monsters who eat people. Lately, Saya is beginning to think that there's a lot more to the situation with the Old Ones than she knows...

Noda Haruko has hatched a plot to get tasty lunches; she's put a love letter in a paper airplane and tossed it out into the world. By chance, it ends up in the hands of a lonely boy named Katou Seiji. Haruko confesses her "love" for him, and her hope that he'll become her husband and make her delicious lunches. Surprisingly, Seiji agrees, and becomes her boyfriend-chef. Seiji allows himself to be swept away by her childish enthusiasm, but he keeps trying to find ways to make their relationship more 'real'-- by holding hands, kissing, or simply being alone together. Haruko and Seiji navigate their unusual relationship among their friends and classmates, who all have their share of comedic troubles!

Kenmoto Kazuki is a 15-year-old high-school student who is late for school on his very first day. As he's running to school he sees someone on top of a wall that warns him not to go through the main entrance. Without a second thought he blurted out three words, "Please marry me!" From the shock the person falls off the wall where Kenmoto Kazuki discovers he just proposed to a man. This man was not just any man, but Morikeoke Akitou his homeroom teacher!

The midsummer sun's rays enter the courtyard. Umehara of the school's art club is commanded to do weeding as a punishment with Mizue, a classmate he doesn't get along with. It was supposed to be the worst scenario Umehara could find himself in, but he begins to have a crush on Mizue and cannot tell anyone about it. Suddenly, Mizue asks Umehara, who puts his feelings into his paintbrush, to draw a picture of him...?! The two of them end up spending time alone in the art room after school. What is he to do with the feelings for Mizue that he can't suppress?

1-3) Love Minority
Isuka Yoshihito, a high school infirmary sensei, fell in love with a student, Shiina Satoru. However, after Sensei confessed to Shiina-kun, things started to go wrong. The mild-mannered Shiina became totally different and their strange relationship began.

4) Evening Grew
A high school reunion brings back memories for Hayashi Akira when he sees his childhood friend Tsujitani Masato. While Masato was easy-going and popular, Akira was quiet and deep and his intense affections and jealousy for his friend led him to destructive actions that would haunt him for years...

5) That Future that is Unknown to Us
At junior high graduation Kazuki confessed to his friend Makoto, only to get shot down. They've managed to hang onto their friendship, even though they go to different high schools. But lately Kazuki's love-em-and-leave-em gay relationships are starting to bother Makoto.

6) Paradigm Shift
Love Minority extra.

Collection of 8 oneshots.

1. Tokimeki and Suki and Kiss
Things get complicated for Tetsu when his childhood friend Makoto confesses that his penis gets erect when he's around Tetsu. Tetsuhito starts thinking about things, and wondering if he can get erect for Makoto too... well there's only one way to find out, right?
Note: They are both high school students, even though Makoto acts+talks like a child, so this ain't shotacon.

2. I'm Thinking About
Matsushita-sensei tells his lover, and student, Atsushi not to come over until exams are done. The separation proves to be harder than Matsushita thought...

3. My Stuff's Gone
Tsukasa and Hideomi are childhood friends. Hideomi has been pulling Tsukasa into certain naughty behavior. Despite Tsukasa's reservations, he went along with it, but then Hideomi's shocking declaration of "I want to try having sex"?! And on top of that, a confession...?!

4. Look In
Mayama's in trouble. Okabe caught him staring... and confronted him about it, asking if he's gay. Mayama runs away from his classmate, but what happens when Okabe catches him staring again?

5. Gotta Love It
Mizuno has been hurt in love before, so he made the decision to never date another man again. But when Tomoya, his home-tutor student, professed his love for him at first sight, Mizuno finds it hard to stick to his plan. Will Tomoya's feelings get through to the Mizuno's locked-up heart?

6. Knight Applicants
Masato is prince at his school as well as being the student council president. His guard is his loyal childhood friend and Vice President, Kei. Masato confesses that he has someone he likes, although it's one-sided. Kei finds himself more shaken about it than he had expected, but has no time to think about it, as someone is after Masato...!

7. Moon's Magic
It is often said that long, long ago, the moon and cats had a very intimate relationship... But what exactly does that mean?

8. Referred to You
Fumio's grandfather liked to collect strange objects. Among these was a lamp that one day Fumio decided to clean. An adorable genie appears, saying that he will grant Fumio three wishes. Fumio's first two wishes come and go accidentally, but he decides on a kiss from his favorite poster girl to be his third wish. Just as he asks for the kiss though, the spirit of the lamp misunderstands... But actually, this feeling isn't bad...?

All the characters look like children/young teens, although they're adults. If you don't like shotacon, you might want to skip this one.