Based on the visual novel by Enterbrain with the same name.

Note: This manga focuses on all of the girls at once, instead of different arcs.

I gave a guy I didn’t like a love potion? Hong Yoo, quarreling with top star Ji Sulwoo due to a wretched first meeting, fed Sulwoo a love potion one day. That shady love potion…did he really drink it?!

Sakaki, the president of an interior designing company, is determined to never get serious with anyone - fearing the heartache he feels that it is sure to cause.
Much to his discomfort, he realizes that he is beginning to fall in love with his older heterosexual co-worker, Okada.

Sakaki is shocked when he finds himself in Okada's home one day, with no recollection of how he got there. At first convinced that he did not act out-of-line at any point, Sakaki feels more and more unsure of this as he notices the changes in Okada's behaviour towards him.

Will this storm that's brewing on the horizon ever calm down?

(Sakaki also appears as a minor character in Signal, a story set two years prior to the events in "After a Storm")

Takatoki is a high-school boy with an intense obsession for manga and anime. He desperately wants a typical anime romance with a girl who falls into a typical female anime stereotype. His childhood friend Chiyoko, a very unladylike girl who is a notorious fighter, tries in vain to get his mind back to reality.

One day, the two of them run into a girl in a sailor schoolgirl outfit being threatened by a generic band of thugs. As Chiyoko beats up the thugs, Takatoki learns that the girl, Asadzuma Youtsugi, is a cosplayer who wants to lead the life of an anime character. Was this Takatoki's fated first encounter with his future anime lover!?

"In a Fight, they say that the first one to bleed from his or her nose is the loser. Father, Mother and Brother...They're all LOSERS that bled from the nose facing that damn monster called WORLD!

I'm not going to fall into that one. Even though I have to break my head, I'm not going to bow my head before anyone. I'm going to finish everyone! I'm going to throw everyone on the ground with the "Ushi Mata".
Even though my opponent is...a GIRL"

The Boy that doesn't bow his head to anyone...
SUK DONGMIN

Set within a ravaged world, a girl protects the people from these monsters is interwoven into this mysterious fantasy.

This is a oneshot from the Moonsorrow Collection II.

"Originial" doujinshi by the circle Moonsorrow.

From ADV:

A mysterious creature has fallen from the sky and landed right at young Yuina's feet! Branded as the master of this new angelic being, Yuina is forced into an otherworldly pact, one that will take her beyond the clouds and into battle against a new and yet hauntingly familiar evil, one that patiently waits in the shadows.

From ShoujoMagic:

"Forgive me. I can't become a servant of the Lord yet," Maria says as she runs from her vows ceremony at the convent where she was orphaned 16 years ago. She has received another letter from the mysterious "G," her faceless benefactor. She is not as alone in the world as she thinks; "G" writes that she has a relative at Hakuhou Academy who is in need of her guidance, but he cannot tell her this relative's name. Trying to enroll and search the school presents Maria with a number of problems, however -- the foremost of which is: Hakuhou is an all boys school!

A legendary dragon once brought the land of Astoria to the brink of ruin. He was defeated by a man named Yurius, who was soon supposed to go to his princess and live happily ever after. However, with the last of his strength, the dragon placed a curse on Yurius: all his memories will be erased, and his body will turn back to a child. It is now the goal of a novelist, Elliot, to return Yurius to the courageous person he once was.

The story revolves around a mysterious place called "Angel's Island" that resides somewhere on the ocean seas. Living on Angel's Island are a species of merpeople that can live in both the sea and on land. They have the form of a human, but can breath in water as well as on land. Luna is a princess of this species of mermaid living on Angel's Island, but is exiled for breaking some of their rules. As punishment, she is placed inside a sea shell, and set adrift across the sea. Meanwhile Eiji Kusahara, the son of a wealthy Japanese family, meets Soleiu (Luna's older sister) and they try to discover the mysteries behind Angel's Island.

From MangaArt:
The story begins when Hui-Sheng, a seemingly ordinary high school girl, receives a deck of angel cards from a mysterious stranger, Jason. With the angel cards, Hui-Sheng attempts to find out who her guardian angel is. But the result of the reading (a blank card) shows that she has none...

Shiina Amane is special. Her father is an exorcist, and she herself can see spirits. But gifts always come with a price.

The series takes place in a universe parallel to City Hunter.

A young Taiwanese assassin codenamed "Glass Heart" committed suicide by jumping off a building, and her heart was pierced by a metal fence. Miraculously, her life was saved by heart transplantation. During her recovery she began to experience strange dreams, which led her to Japan looking for the donor of her heart, who happens to be Kaori Makimura, former partner of City Hunter.

N/A

When a devastating meteor struck Earth, Earth's guardian angel Lyu was so tortured by guilt that she killed herself. Mo Ye, the demon who was in love with Lyu, is determined to find her again. Has he found Lyu's reincarnation in the human Xiao Tian Nu?

Tomoki, a high school student lived with his older sister. What happens when a normal boy has to put up with his sadistic but popular sister?

The one thing not ordinary about high school student Ryouta is that he has an aspiring manga artist for an older sister. She is so dedicated to her drawing that, despite being 21, she's never really been in a romantic situation. Unfortunately, when she gets her first real job, it's to write an erotic manga. Desperately, she enlists the reluctant Ryouta's help, as a 'model', to figure out how exactly to draw this sort of manga.

The girl, Mana, has no problem with seeing the scenes she plays with her brother as nothing but a hollow reference for her works.... But she fails to realize that her brother seems to become more and more flustered with each 'live performance'.

Rosie's mother loved her father till the day she died... even though he abandoned her when she got pregnant. Rosie wants to tell her father how her mother felt, so she goes to work at her father's mansion as a maid. However, her father isn't there. Instead, a sexy man named Sebastian meets Rosie. Rosie is won over by his kindness, and before she knows it, she ends up in his bed. Will Rosie now share the same fate as her mother?

Shirafuji's feelings of physical intimacy between him and a classmate, Arisaka, are piling up. He wants to know how Arisaka truly feels about him, but he doesn't have the courage to ask, without exposing his "true feelings." He is terrified of getting hurt, even a little, but now it seems that his love is about to lose sight of reality.

Two couples from this volume have sequels in another of her works Agetai Kimochi.

Arisaka x Shirafuji from ch1 here and ch8 in Agetai Kimochi.
Eiji x Yuusuke from ch7 here and ch2 in Agetai Kimochi.

Chapter 5 is hard shota content, and not scanlated for that reason.

A short 26 page story about a student-teacher relationship. The teacher breaks it off and after 6 years pass, the student is now a teacher also and they find that their feelings are still the same.