When Ryuuta was 6 years old, he was attacked by a youkai. At that moment, a mysterious boy named Izumo came to his aid and exorcised the youkai. Izumo gives a promise that when Ryuuta gets strong enough to be by his side, they’ll meet again.

After 10 years, their paths cross once more. But it seems like Izumo doesn’t remember Ryuuta or their promise! When a youkai threatens the village, Ryuuta tries to help but Izumo ends up getting injured. At that moment, he transfers some of his power to Ryuuta...with a kiss! Together, they exorcise the youkai, with Ryuuta vowing to protect Izumo from now on and following him on his travels!

(Note: “Yokai” are supernatural spirits or monsters in Japanese folklore.)

From etc:

“Things that should not be touched by humans somehow find their way into this world. That’s why you should never, ever touch anything that is foreign.”
Follow the adventures of March, a Syste Behard, who hunts ils– evil creatures that lurk in fascinating objects.

Among the quiet villages and towns of 18th century Europe, demons known as the Ill hide within the most beautiful works of art, sparked to life by the torment of their creators. Attracted by their jewel-like allure, the unwary find themselves possessed by the Ill and driven to horrific acts of violence. Only the hunters of the Ciste Vihad can dispel the Ill.March is one such hunter, tracking the Ill from town to town to find the antiques that contain the demons before they can possess anyone. If the worst has come to pass, March's full powers are unleashed to battle the fiendish Ill. Born of tragedy, the artifacts all have their own tales to tell, as do each of their victims. But March's story may be the most tragic of all.

Newman and Gwen are professional monster hunters who work for the Creature Removal Department, but for these two, killing monsters is the easy part, it's navigating their relationship that gets complicated. Set in a modern fantasy world, Newman is a mix of comedy, action, romance, and a little bit of horror.

Yokota and Mishima are art students at a University. One evening, everyone goes out drinking and Mishima ends up in a car accident. Taken to a hospital, his body is on the brink of death. But, his soul pops out and ends up trapped in a studio room at the University. He won’t die because there’s still something keeping his soul connected to this world. Yokota is the only one able to see and touch him, so he has to help Mishima put his soul to peace.

Myoujin is a guide for spirits. Unlike most people, he can see ghosts, ghosts who live and wander in the same world we do. But he's got something even more special up his sleeve: he can touch them. Okegawa Himeno is an ordinary 16 year-old girl studying in Tokyo. But now she's become Myoujin's housemate, infact, he's her landlord. After a close brush with death herself, Himeno becomes able to see the walking dead herself. At least now she's able to meet her neighbours.

A series of mysterious murders without injury are happening in Tokyo, how will Kumoi Soutarou react to them? A Oneshot from Miracle Jump!

From DrCoke at MangaHelpers:
A detective hunts for clues on the impossible "alibi" of the mysterious girl, a suspect for the murder of her own parents, who testifies that she has the uncontrollable and spontaneous ability to transform into literally anything. This collection of short stories is filled with mysterious and fantastic plot, introducing you to the fantasy worlds of Kawaguchi Madoka!

To gain the confidence to confess his love to his crush, high school student Yashiro visits a secluded shrine for 100 days straight. This earns him the attention of the enshrined deity and his fox attendant Ukon who follow Yashiro on the 100th day to see how the confession turns out. However, they are surprised to see him confess to a guy, Yashiro's longtime friend Kenta, only for Kenta to turn him down. Although heartbroken, Yashiro tries to joke around with Kenta, but he accidentally gets killed when a truck runs into him.

Yashiro awakens in the presence of the shrine's god and Ukon, and as a show of gratitude, the god decides to restore him back to life to give him a second chance with Kenta. In doing so, the god grants his wish to be reborn as a high school girl and gives her the name Kagura Tendou. However, she soon discovers that the god and Ukon plan to watch over her relationship with Kenta, although she's the only one who can see and hear them.

A spin-off to the popular zombie manga I am a Hero, set in Nagasaki.

1-2) Bokura wa Minna Uso Bakari

3-4) Kamiato ni Pride

5) Fuhoni Nagara Hodosarete Shimaimashita

6) Utakata Koi Zoushi

A collection of oneshots about monster girl wives (and more!).

Hajime Sorajima's got a terrible hairstyle! It's so weird it's downright embarrassing. But his hair's got a secret...it's not hair! It's the horns of an alien body! A cute little alien body! One that can transform into a human. Normally, he has no problem living among humans and his secret is safe. That is until he meets a strange girl named Ria Aiba who's convinced he's an alien! Will she blow his cover?

Various unrelated oneshots by the mangaka.

Tears of Pearl has an extra contained in volume 7 of Sayuri Hime called Summer With a Mermaid

Flower of My Heart has an extra contained in volume 7 of Sayuri Hime called Flowers in the Shade

During the Qing Dinasty Era in Shanghai Korin works as a prostitute but what occupies her nights?

From Lezhin:
Hearing that his sleeping disorder can be cured by sleeping naked, Hojin decides to try it out. Little did he know that a ghost was living in his house. Little did he know that the ghost was a girl. Little did he know that the ghost was into his naked body.

Kuromine is a guy who does not lie, hence his nick name "a bag full of holes". But everyone has secrets, and even Kuromine has one. Meet the very lovely, elegant, and mysterious Shiragami whom Kuromine has new found affections for... But what is this? Why does she have humongous wings when no one's looking and super long canines? Something is very different about this girl...

Hataraku Maou-sama! with a high school setting.

Every man who encounters Tomie becomes obsessed with her and eventually kills and dismembers her. But Tomie is not human, and always comes back...

Notes:
1) There is a third volume of Tomie called "Tomie: Again" which was included in the new japanese reissued two- volume version of the Junji Ito Horror Comic Collection (伊藤潤二 恐怖博物館). These new stories are not included in the original ComicsOne editions of Tomie, but are available in Dark Horse's Museum of Terror volume 2.

2) Besides Junji Ito's Horror Comic Collection (Also called Museum of Terror), in 2000 Tomie was also published in a compilatory tankoubon called "Tomie, The Complete of Tomie" -「富江」 （全）THE COMPLETE OF TOMIE-. Regardless of the title, this volume does not include "Tomie Again" within its pages.

3) Some people also consider "Tomie no kyoufu gaka" [ シリーズ富江の 恐怖 画家] as part of the Tomie franchise. Tomie no kyoufu gaka was the first Tomie's compilatory tankoubon that was ever released (It was published in 1996) and features five stand-alone stories (Gaka, Ansatsu, Mouhatsu, Youjo and Takitsubo) that were published a year later in Junji Ito's Horror Comic Collection.

In modern Japan there are seven "Kings" who share power with their fellow clansmen. The Blue King Reishi Munakata, the leader of the Blue Clan "Scepter 4," held great responsibilities on his back. The tower that Gold King Daikaku Kokujōji supervised called the "Dresden Slate" was still on his mind, and he felt a great burden by killing the previous Red King, Mikoto Suoh. On the other hand, the former Red Clan "HOMRA" clansman Anna Kushina experienced the attacks from the Green Clan "Jungle" and awakened as the next Red King. By doing this, she bound her comrades through a strong bond once again. Finally, White Clan members Neko and Kuroh believe that the White King Yashiro is still alive, and seek his whereabouts. However, it was not just them searching for the White King. With "Jungle" once again jumping back into action, the fates of the various Kings are brought together.
from ANN

This is Kayono's first volumized collection of short stories, and all of them center on tales of strange worlds.

1) Ostentatious Mysterious Handsome Man (Rei Kai Bi Dan)
Momoe hates to go home, so she spends her nights wandering the streets. But what happens when she meets a man named Chain Saw who's on a special mission!?

2) Ancient Osaka Masquerade Ball
Naniwa Masquerade: Frustrated that her childhood friend Yuan won't look at her like a woman, Ai goes to a host club, and there she finds what she's been waiting for...!?

3) This Love by Anonymous
Asuka is afraid that she'll be forced to become the lover of a man whose ideals are far from her own, so she runs away to Kyoto. There, she falls in love with Takuma, a high school student who's in Kyoto on a field trip.

4) Like a Beautiful Hellish Demon
Naoka is beaten so badly by her stepfather that she loses consciousness and has to be taken to the hospital. There, she meets and falls in love with a hellish demon who feeds upons the souls of humans...