In the Docchi mo Docchi series:

V.1 - どっちもどっち Docchi mo Docchi
From their offices high up in a corporate skyscraper, alpha males Ozaki and Tsuburaya make all the ladies swoon. Ozaki's known for his irresistible pheromones, while Tsuburaya's a noble, worldly genius. But when these two rivals end up in bed together, who will come out on top? It's seme versus seme...and much more than pride's on the line!

V.2 - どっちもどっち! ! Docchi mo Docchi!!
At long last, the battle to become top dog - literally - produces a clear victor. But who will it be?

V.3 - どっちもどっち! ! ! ~第三のイケメン~ Docchi mo Docchi!!! - Daisan no Ikemen

V.4 - どっちもどっち！！！～厄介なイケメン～ Docchi mo Docchi!!! - Yakkai na Ikemen

V.5 - どっちもどっち! ! ! ~覚悟のプロポーズ~ Docchi mo docchi!!! - Kakugo no Propose

V.6 - どっちもどっち! ! ! ~ないしょの遊び~ Docchi mo docchi!!! - Naisho no Asobi

Nonaga Hiromasa is an up and coming soccer coach who has made a name for himself for bringing multiple teams from literally nothing to the top in the country. What’s even more impressive is that he just entered high school! He was recruited into his current high school as the new soccer coach, and his observation skills and ability to predict the opponents’ movement make his sole presence enough to win games.

The fact that Hiromasa is going to be coaching at the high school has many top soccer players flocking to this school, but none stand out more to him than Sakamichi Kappo. Not only can Kappo score a goal from half field with his powerful kick, but his ball control is second to none. Initially, Kappo didn’t want to play on a team because he thought no one understood “his soccer style,” but when Hiromasa was able to understand it, Kappo decideds to play for the team. Will the brilliant coach and the talented player be able to take the high school soccer world by storm?

In a school where after school activities are mandatory among all students, Hajime and her friend Sayo come across a new club that they have never seen before. The club is called "The Cultural Activity Preservation Club." The two enter the room to find all kinds of analog jobs and activities, such as handcrafting mats and toothpicks. This is a unique cultural manga mixed with comedy so as not to bore you, this is Double J!

The story follows Erina's route in the Dracu-Riot game. Erina is a foreign vampire from Russia and she is very ecchi, her conversations often involve ecchi stuff which makes Azusa really edgy and Yuuto nervous.

A collection of Dragon Kishidan oneshots and side stories:

One Day, Another Day
Set before the end of the series, it's basically a side story of a day in the Dragon Castle, kind of in Zoma's perspective.

Juuji ni Hikaru Hoshi
Takes place before the events of the actual series. This is a back story that shows how Lykouleon and Raselane met, introducing Lykouleon's uncle, Fieruto.

Mamono no Mori no Kioku
Another backstory that delves a little bit more into the relationship between Bierrez and Cesia before the series started. It also shows how Nadil became the demon lord.

Happiest Children
This actually has three little side stories in it. The first one is about Rune's dream about everyone dressed in drag, the second is about a little adventure that the three dragons go on, and then the third is like a day in the life of Alfeegi, Ri-ma, and Duma.

Crescendo
Backstory about how Lykouleon and Kaistern met and how Kaistern then became the Blue Dragon Officer.

CONFESSION - Thats
This is basically the backstory of Thatz and how he knew about Rath's little secret.

CONFESSION - Rath
Basically telling a lot about Rath, particularly his relationship with Kaister.

A collection of mildly ecchi otokonoko-styled stories focusing on crossdressing high-school boys and the boys who like them, mostly from the men's magazine Oto Nyan. Some of the stories are continued in Hiriajuu Shuudan ga Classmate o Josousasete Kanojo ni Shite Mita.

1-3. Raising Decoy
A boy helps his classmate go undercover in drag to catch subway gropers, and finds that he looks disturbingly good in a dress....

4. Ato no Matsuri (retitled Spilled Milk in the English edition)
A group of male students, having failed to get girlfriends, are becoming desperate; what will these "innocent" boys resort to?

5. Tenshi no Houbutsusen (Parabola)
Baseball-themed romance short.

6. Actress
A boy joins his high school's film club to meet the actress from their amateur film, but gets a surprise...

7. Shishiza no Boku to Natsu no Yozora (retitled Leo and the Night Sky of Summer in the English edition)
The president of the school astronomy club wants to catch UFOs.. maybe some "sexy female alien" costumes will help?

From Day of the River: “The person who killed my father...is among these people.” 15-year-old Kotobuki Ringo reunites with childhood friends she hasn’t seen in eight years since her father passed away: the calm and soft-spoken Shiran, the strong Kujyaku, the kind Masaki, and the energetic Gogyo. They were all students of Ringo’s father and all have amazing abilities of their own. Ringo comes to live with them at Shiran’s villa, but she’s not staying with them just to rekindle their friendship... She believes that one of them may be her father’s murderer, and she will stop at nothing to find out who was behind her father’s death.

From Yuuki Megane Scans:

Shuuhei, Harumi and Daiki start their second year of high school with an absolute goal: Getting at least two new members for their swimming club to keep its position as a club. This is the daily struggles and shenanigans of a high-school boys' swimming club!

From DrMaster:
After his mother's death, Kuro Takagi transfers to Yotsuji Private High School where his father is the proprietor. But Yotsuji is no ordinary school. It holds a strange rule of “No students on campus after dark!” On his first day of attendance, Kuro and his classmates inadvertently break the school’s highest protocol and find themselves victims of a faculty zombie attack. Although they manage to narrowly escape, this is but a prelude to more encounters with the undead, especially after Kuro discover his own blood-ties and latent zombie abilities. From there, it's full steam ahead as this dark and intense action/comedy shifts into high gear.

Sagetsu is the only successor in the family of "Super-angels", beautiful heros of justice. He masks his identity and pretends to be an ordinary high school student, but one day a news photographer, Yousuke Zama takes a picture of him as Super-angel...

Also contains a PWP side story about a boy who transforms himself to super hero by semen.

1-7. Colorful Hayate no Gotoku!
8-16. Hayate no Gotoku! Limited
17. Hayate no Gotoku! Dai ?-wa (Hayate no Gotoku! Chapter ?)
18. Hayate no Gotoku! Prototype
19. Hayate no Gotoku! Variety

From Intercross:

1. Bokura no Himitsu o Kyouyuu Shiyou ka
Yuka goes to Ikimonogakari's room to ask them to solve her love problem, but unfortunately, they couldn't help her. To make her feel better, the people in the club gives her a piece of candy. Yuka eats it, and she suddenly gets cat ears and a tail! What happened to her? Will she ever go back to normal?

[T/N: Ikimonogakari literally means "(person) in charge of living beings"]

2. Colorful Shounen to Monochrome na Atashi
Naoki and Kiyo have known each other for a long time because they live in the same apartment complex. One Valentine's Day, Kiyo gave Naoki a chocolate cake, but Naoki threw it away and laughed it off. Because of that, Kiyo doesn't make sweets anymore! Because Naoki's dad is Kiyo's dad's boss and they are going on a trip, Kiyo has to make food for Naoki. Will Kiyo re-live the trauma of the past?
(Also included in the Sweets Fortune Telling Anthology as Boy of Macaroon story)

3. Kaibutsu-kun ni Rei
At the Christmas training camp, Yuzuki was paired up with no other than... that guy?!

4. Itoshi no Himeko-chan
Anri, who is usually bad at handling boys, is asked out by the school's most attractive guy, Takuma! This is so she can gradually get used to guys, however, does Takuma have another agenda in play? What is going to happen between the two?

5) Shiro no Kiseki

From Forbidden Garden:

1) Cream Caramel
Because her parents are transferred away due to their jobs, Mikoto, a grade 11 student, starts living alone on 100,000 yen per month. But the place she lives at is a horribly old apartment... And the one living in the room next to hers is a super cool boy...?!

2) White Summer
Mana and Shou have to go their separate ways after graduation, will they be able to stay together when they're hours apart?

3) There Are Days Like That, Too
Sonomi has been in love with Ikuta-san since she was in the seventh grade, four years before this story takes place. Ikuta-san suddenly starts working at her uncle's cafe, and it seems like Sonomi might have a chance to be his little sister, since he's been going out with another girl for those same four years that she's loved him.

From Dan of Population GO:

Ooba Asa woke up one morning and became an invisible man. It isn't just him, but various students around school have been gaining superpowers while his little sister has been losing the same powers. Supposedly the student council president is giving out superpowers, Ooba Amime's powers, so Asa, Amime, and the grudge-filled flame girl, Daimon Yaki, form an uneasy alliance to give the mysterious student council president.

Contains 9 stories pertaining to love and friendship.

1. Kimi no Nokosu Toumeina Ao
Two friends spend their last summer days together before one of them moves to a completely new town and school.

2. Okama Kata Emban
A student secretly pines for his teacher. A fellow student advises him to confess, but with graduation fast approaching, he might not make it in time.

3. Hole Memories

4. Promise

5. I'm Real

6. Daisuki Daisuki
A clumsy and highly optimistic student develops feelings for his classmate. While he thinks there is absolutely no chance, it may take an unexpected event to prove otherwise.

7. Nearly Drowning My Honey~

8. Sweet Harvest

9. Confession Day

In order to become a splendid devil in Hell History, a stubborn and reserved 6 year old, Robin Verall, will be entering Hell Academy elementary. He really hates to go to school so he hides in some weird places, resulting in him "being in a pinch!" Robin's homeroom teacher, Shiba-sensei, discovers him in an odd place and saves him from a pinch, and since then, Robin is feeling a bit more attached to sensei than ever. And goes through some Hellish schemes to tries to get closer.

From a place in a different dimension from Earth, a world called 'Lote'. It is a world of androids, comprising of a queen, princess, rook, bishop, and knights under the command of a main computer. However, one of the main computer, the princess suddenly disappeared and the world of Lote falls into chaos. In order to find the princess, the head of secretary, Dion, travels to our world, Earth. There, he meets a high school student SeoYoon, and from this incident the life of SeoYoon takes a 180 degree turn...!! - Translated by Grumpy from Naver Manhwa

From Ivyscan:
Aika is an ordinary high school girl. She likes memories and photography. Those things involve her in an unexpected incident.
A tough guy at school wrecks the lens of her camera and she demands that he fix it. They end up skipping school for the day and...

Included in Otoko no Ko Comic Anthology: Zettai Fukujuu-hen.

Michi is a girl given extraordinary power by her fairy godmother Yaaba...the power to transform into the beautiful and heroic Cinderella Knight. With these powers, she seeks to protect the man she loves from afar, the handsome Prince Emilio of Ballade, from the evil Spider Corps of the organization "MURDER"