There’s one thing I understand when I became an adult.There’s nothing special about boyfriends, sex and kisses. but if I think that, will I be able to find love?

From Lililicious:

In "24, 25," the main character reminisces about a girl she knew in high school.

1-2) Can't Kiss for 24 Hours
A math teacher who has an intense relationship with the problem student, Kikusui Kiyoya. Even though they were a couple in love, one day, Sensei suddenly wants to break up...?

3) If I Didn't Have You
Fujisawa Yuu just moved to a new town. On the first day of school he's warned to stay away from Nanatsuki Haruki. The word around school is that Nanatsuki who is actually 20 years old will sleep with anyone, but only at school. The mystery is why he only sleeps with people at school and why hasn't he graduated yet?

Humanity, having faced extinction at the end of the 20th century, would not have entered the new millennium if it weren't for them. In 1969, during their youth, they created a symbol. In 1997, as the coming disaster slowly starts to unfold, that symbol returns. This is the story of a group of boys who try to save the world.

Won the Kodansha Manga Award in the category "Best General Manga" in 2001.
Won the Seiun Award for Best Comic in 2008.

From Anime News Network:

A collection of short stories that look to mankind's exploration of space, and examine the possibilities that we could face when we decide to take those first fateful steps into the unknown.

From Tokyopop:

Akira - who later appears in the CLAMP School Detectives manga series - is a dapper, debonair young thief-for-hire who becomes the object of 5-year-old Utako's affections.

From Boys On Boys Love:

1-2. 2-dome no Koi no Hajimari wa
After being harshly dumped by his lover, Kousaka Yuuki, a shop manager at a restaurant, swore that he would never love again. One day, he meets his ex again when he unexpectedly shows up at Kousaka's shop. It was then completely exposed to Matsuoka, a kouhai at work, that he dated a guy. Kousaka was shaken that his past was known to Matsuoka, and worried that he would look down upon him, but Matsuoka forcibly kisses him and says "I love you" to Kousaka...!?

3. Gekiai Honey
Sasaki Ryoutarou, a part-timer at a restaurant leading an ordinary life, suddenly met his old classmate, Mio. Mio was once a gloomy guy ignored by all, but is now a cheerful, completely changed guy. He claims to have been searching for Ryoutarou to be his lover because he couldn't forget about him, even after being rejected a long time ago. Mio changed his style because he had heard that Ryoutarou's type is a cheerful person. Ryoutarou refuses to go out with him, to which Mio responds: "go out with me for a month, if you don't fall in love with me then I'll go back"...

4-5. Honey Trap
You is in love with his best friend Shinji. Afraid of ruining his friendship with Shinji, he doesn't confess, and breaks off all contact with him. Three years later, running away from some stalker, he enters a building and asks for help. However, it turns out that the man living there is his ex-friend Shiniji, who is now a detective...

But what will happen when Shinji suddenly asks You to be his lover?

6. Bokura no Koi no Hajimari wa

- Extras
Is a small continuation about the first story.

N/A

Ikumi and Kunitachi are finally hitting it off steadily. However, trouble starts once again during Valentine's Day when Ikumi received a box of chocolates containing glass and became the victim several other pranks. In the end, when the person revealed himself to Ikumi, the past was unfolded.

Unconsciously jealous over what he's afraid to know, Ikumi threw a fit and said something cruel towards Kunitachi. Unable to take it, Kunitachi raped Ikumi...

A collection of stories:

1-3. 2 Shuukan no Adventure

4. Himeko-chan

5. His Left Eye
A story detailing an encounter between Gerry and Eugene from Barairo no Hoo no Koro, as adults.

6. Belgian Waffle
Andrew, from Barairo no Hoo no Koro, takes a stroll with his old father, bringing about some surprising discoveries, aside from the fact that Belgian Waffles can be sweet.

Timeline (from Oriolidae & Sparviero):

01 Barairo no Hoo no Koro v01 ch01-05
02 J no Subete v01 ch01-05
03 2 Shuukan no Adventure v01 ch05-06
04 J no Subete v02-03
05 Barairo no Hoo no Koro v01 Extra

From Chibi Manga:

5 years ago, Shin was Yumika's private tutor. Now this Shin-kun comes to Yumika's high school as a teacher trainee! But their love from 5 years ago will most probably start to bloom again?!

From Midnight Scans:

Yumika’s first love was her tutor Shin. As she hope to meet Shin once again, which really happens, how will Yumika proceed on to confess to Shin about her feelings…

From Beautiful Soup:

"1999" is an angsty and widely varied series about a bunch of teenagers. One of them is the son of a drug lord and so as you can imagine, all sorts of shit goes down, surrounded by a backdrop of convoluted and fluctuating interpersonal relationships.

This is a plot heavy manga with some mildly-explicit sexual activity.

MAL:
This plot takes a new twist to Romeo and Juliet's forbidden love. It's July 7th, 1999 in Shanghai and there are two gangs fighting for control. Only in the ceasefire zone do people live in peace. In a chance meeting Xiaoxue, who is part of the Toulon's gang, and Dawu, from the Xianglongji's gang meet by chance and without knowing they are enemies. In the heat of the moment Dawu takes him to a place he has the keys to in hopes Xiaoxue will join him, but is turned down. With a simple kiss he leaves Dawu not knowing they will meet again, but in very different circumstances

1) Water Breath
An injury destroyed Olympic hopeful Ryuji Hayashida's promising swimming career. He was transferred to a university where he believed no one knew who he was, but he was wrong. There was someone who recognized him the moment their gazes met at the university's swimming club.

2) Pension
A tempestuous tale of a rock band and the consequences of their enigmatic guitarist's return. It didn't take long to realize he has a keen interest in their lead singer.

3) Dance
Shachi never got over his feelings for his classmate Michio who jokingly danced with him at school. Years after their school graduation he discovered what Michio did for a living. The discovery inspired him to sell his father's car for one night with Michio, which turned into a different kind of dance.

4) Longing
Shy and timid high school student Sakaki has always watched his classmate Ryoji from afar, but he wasn't as invisible as he believed himself to be.

The student council president is gaga over the vice president, but her feelings may or may not be returned. In the meantime, it's up to the serious and by-the-book vice president to keep the flaky (but surprisingly effective) president on track.

A sixteen page seasonal short! Futaba, the loneliest gay student in the world, has a crush on his best friend, Toki. But Toki is straight, and Futaba will never do anything to mess up their friendship...

After she died from an accident, Ria become angel No. 5623. She could not forget her life from when she lived. She misses Ban Ji Hwan, her boyfriend on Earth, day and night.
1 year later, Ria happened to see Ji Hwan's name on the death list, the list of every names who is about to die in 100 days. Ria begged high-ranked angels to let her save Ji Hwan. Ria entered the body of So Hae, a shy girl who is tired of her life, the opposite of Ria's personality. Enduring the bullies from step-siblings of So Hae, Ria did her best to bear everything in order to look for Ji Hwan. But when she found him, Ji Hwan cannot recognize Ria...

An art college students moves in Venice to study, she starts to live in her new room, part of an old huge historical mansion and she discovers a new world of secrets linked to her young, mysterious landlord. A gothic romance story and a vampire tale which flows around Venetian laguna and roman museums; a manga rich of suggestions and images with a passional storytelling, a deep noir drawing style and melancholic mood. From Italians to Japanese. This was created for Kodansha, published on Amie. You read it Japanese style.

Kazao is happy with his life on Mirai ("Future") Island. Sure, his parents abandoned him after he was born, leaving him to be raised at the orphanage-like facility, but his life is comfortable and has his friends, especially the lovely Eiko, the girl he loves. One night, however, he has a horrible nightmare where he sees himself die in a motorcycle accident. After that, everything changes. The next day, his parents are miraculously "found" and he is torn from his idyllic life and Eiko's side to be thrust into a world he knows only from television shows and school assignments. Dropped unceremoniously in the middle of a city with only a sketchy map for guidance, Kazao is saved from wandering aimlessly in search of his new home by the cute and forward Yuu, who turns out to be in his class at his new school as well. Despite his best efforts to accept his parents' sudden return and Yuu's friendly overtures, Kazao can't shake the feeling that things aren't quite right. Nor can he forget Eiko. Why did his parents wait sixteen years to call him back? And why is the piano the only used piece of furniture in his parents' new house? The mysteries begin to pile one atop the other as the lies fall apart in this intriguing story of future possibilities and innocent romance.

From Dark Horse: A vacation fling was completely out of character for old-fashioned Carol, but her attraction to intriguing, older Marius tempted her to break her own rules. The next thing she knew, though, he'd turned up working at her hospital! Does she have what it takes to attract-much less keep the attentions of-this intimidating, sophisticated, and utterly compelling man?

Kei is interested in a woman at the gym. Imagine her surprise when she sees her in a lesbian bar!