Ever since she was young, Nonoka always dreamed of watching the end of the year Countdown with a boyfriend. Now that she's in high school, she wants one! However, there's no signs of getting a boyfriend anytime soon, and it's already December.

(Source: ShoujoHearts)

Enren Debut is a one-shot that takes place 11 months after the end of Koukou Debut.

Sequel of Kokou Debut, Enren Debut tells what happens during the Golden Week time after Yoh left for college in Tokyo.
Its been sometime since Yoh left and Haruna had to start another part-time job to keep her expenses in check. In addition her new manager is a total jerk who keeps her reminding that her Long-Distance Love won't last long. What will happen to Haruna's insecurities in her Long-Distance Love Debut?

Summary from An Endless Story: "If you ride a train you can see there are a lot of different people. I wonder where they came from and where they are going. I've been able to hear many conversations and I wonder what kind of relationship these people have. I want to talk to them and ask, but I would be weird if I did so I just enjoy imagining it by myself."

From Viz:

When Haruna Nagashima was in junior high her life consisted of playing softball and reading comics. But now that she's going to high school, Haruna decides to put all of her energy towards getting a boyfriend and having the high school romance of a lifetime. To help in her quest, she enlists cute upperclassman Yoh Komiyama to coach her as she eschews her tomboy tendencies and turns herself into the kind of girl who can catch a guy. Yoh agrees, with one catch: Haruna had better not fall for him!

Volumes 14 and 15 are unscanlated.

A tankobon of some of Kawahara-sensei's short stories.
Includes the stories:
For the Sake of Love,
If Someone Like Me Would Do,
and Chocolate Contest.
Title Story:
Akira is a kind girl who loves to be with her friends. Because of her high success rate in matchmaking, her friends have given her the title of "Queen of Introductions" (Matchmaking Queen)! But for some reason, Aki-chan can't seem to get a boyfriend for herself...an exulting pure love story.

From Selene Scans:
Hibiki and her friends are approaching their last year in high school, and while they both have many crushes Hibiki sticks with one. In the middle of her junior year she falls in love with one of her teachers and learns that love seems more difficult for adults then for someone her age. After learning that her teacher has feelings for her as well, they start to get more into their relationship.

Side story in volume 1: Tomodachi Nante Iwanaide

{Correction from Silvermagic}

#1. Tomodachi no Hanashi (Ch. 1 - 3)
Eiko is something of a plain Jane and a doormat, while her best friend Moe is a head-turning beauty. Despite their differences, their friendship is as strong as ever.
Guys are always asking Moe out, but her answer is invariably "Only if you promise to put Eiko before me."
(Source: etc)
#2. Sono Kare Shirabemasu (Ch. 4)
When a friend up and asks you to catch her boyfriend cheating, what will you find at the end of the chase? Love?
(Source: etc)

A collection of one-shots by manga-ka Kawahara Kazune.
Shiawase no Kanzume:
Emi has been dating Fujii-kun for a month now, but their relationship seems no different than when they were still acquaintances. Depressed that it's still a one-sided love, one day, she gets a prize called "Canned Happiness" from her local town's raffle. Unsure of what it is, she accepts it, but soon forgets about it until suddenly, a small man with a white beard appears in front of her...
Otoko no Ko ni wa Wakarumai:
Hasegawa Shinako has always been worried about her weight. When she secretly finds out that she weighs more than the guy she likes, she vows to go on a diet. Embarrassingly, he finds out and...??
Million Words:
Kitou is dating Kawai, a guy one grade below hers. Although things are going well enough, she still can't help feeling like the relationship will not last. They each have their separate worlds and Kawai will probably notice this soon...
Kawaisa Amatte:
Matsuda has always had a problem saying what she truly thinks in front of people. Once she gets nervous, she seems only able to say the exact opposite words she means to say, especially in front of Tsumura, the guy she likes. At this rate, he will abhor her in a matter of days...
Itsumo Watashi ga Koko ni Iru:
Kawamura asked Tanaka out as a favor to Kondou-senpai. The plan was that Tanaka would refuse, Kawamura would push harder, and Kondou would heroically come to Tanaka's rescue. The plan was NOT for Tanaka to say yes...

I've been watching you attentively from close by... because I fell in love with you.
Only once... although we have spoken only this one time.

(Source: Shoujo Sense)

As a child, Ono Tsubasa saw a Shirato baseball game on TV and was amazed at the Trumpet player in the band playing. Now, in order to play the Trumpet, she enters Shirato High School. There, she meets Yamada Daisuke, a catcher for the baseball team. With each others support, they go towards their dream of playing at Koushien.

A collection of one-shots by Kawahara Kazune.
Tensei:
The day Shinohara Chiaki met Gotou-kun was in April during her second year of high school. The new class lists had just been posted and she was nervous that she would not know anyone. Gotou, the school judo star, instantly introduced her to lots of people and made her feel at ease. To Chiaki, Gotou-kun was like a impressively bright blue sky. But one day, during one of his judo matches...
One and Only:
Matsumoto Rika was on her way to her part-time job as a waitress at a restaurant when in her rush, she yanked open a door right into a guy's face. The guy glared at her in pain and in surprise and embarrassment, she ran away while barely apologizing. She hoped she would not ever have to see him again, but when she arrived at work...
Aishitekurenai:
Fukazawa Akira is dating Yasuda Tatsurou, but Akira is worried that Yasuda doesn't actually like her all that much. It's been a few weeks now since she asked him out, but nothing romantic has happened between them. In addition, she always sees him spending more time with an older friend of theirs named Yuka-chan-senpai, who he had a crush on in the past. Is Yasuda just using Akira to get over Yuka-chan-senpai?

Tsuyoshi Takeo is a freshman in high school. (Both estimates) Weight: 120kg, Height: 2 meters. He spends his days peacefully with his super-popular-with-girls, yet insensitive childhood friend, Sunagawa. One morning, on the train to school, Takeo saves a girl, Yamato, from being molested by a pervert. Could this be the beginning of spring for Takeo?

(Source: MU)