From MangaHelpers:
Humanity has found the perfect energy source that gives the wielder near god-like powers. This energy source has been named "Demon". The rare individuals that have the capabilities to wield this power are known as "Mediums". To become one of the Mediums, Taichi has transferred to the Meissner School. On the first day of transferring into the school, he literally runs into an energetic girl named Nui. She is a Medium and attends the Meissner School. Taichi will require her help to become a Medium himself and survive against hostile Mediums.

Demon Queen Abyss is worried… She's not able to defeat the Hero, considered the mortal enemy of the demons. This Hero is still an inexperienced young man—he should be easy to defeat! … However, the problem is that he, not knowing Abyss's true identity, considers her his “Master” and has become very fond of her…!?

From OSTNT:

It’s said that the Great Demon Lord Satan once went to the world of humans to train, however he was eaten by the humans after he passed out in a desert. Feared of the humans, many demons refused to wander the world of humans. In order to become a Super-Mega-Demon Lord, our prince Lucifer finally decides to wander the world of humans to collect 10 billion devil points.

For thousands of years, the forces of Heaven and Hell have been engaged in an apocalyptic war, which was hidden from the quotidian world. During the first and middle stages of the conflict, the angels were able to eradicate countless demons, turning the tide of the war in their favor. However, demons hold an advantage over angels: they can be re-created from corrupted deceased human souls. As such, Lucifer began gaining more and more ground, until only eight angels (except Archangels) still stand. Given the circumstances, Hell is seen as the inevitable victor.While the soldiers of both kingdoms are able to engage into combat, Lucifer and God themselves cannot, as they are the ones sustaining the very fabric of their respective realms. However, they can visit the quotidian world by possessing a vessel.The fate of the world remains unknown...

A symptom which causes one to physically regress till the point of disappearance. A pharmaceutical company which claims to be researching a cure and the cause for this syndrome. What are their motives? And what does a dragon slayer and even a handful of demons have in relation to all this?

A runaway child who grew up amongst countless bandits and criminals, in a era of the coexistence of demons, in a boundless world that uses devils, spirits and magic.

"So many demon spirits, I want to collect them." Long Ao Tian. Yuan Ding, goes on a journey of collecting demon spirits.

Shota meets loli with wings, the conservative society don't approve of this... and now they are in trouble!

Demons and angels are natural enemies that have grown tired of fighting each other. In order to coexist peacefully, they decided to arrange a marriage between the two races! If the pair can't get along within the one-year trial period, the marriage will be dissolved. This is how Jiacheng (Demon) and Yu Shanshan (Angel) became the chosen "lucky" pair for the marriage. Sharing the goal of divorce, the two began their lives of "happy" cohabitation!

What is it that you desire? Money? Love? Walk again? Be stronger?

Whatever it is you wish for, you can get by asking the legendary and awe-inspiring "Demon's Plan"; a sacred object capable of granting anything to "the chosen ones."

Included one-shots:
Volume 1: Nigashi-ya
Volume 2: Brain Breaker

In the fantasy story, the demon king Leonis sealed himself away for 1,000 years in order to prepare for the final battle, but when he woke up, he found himself in the body of a 10-year-old boy. A beautiful young woman named Lisellia from the Holy Sword Academy then says to him, "Why were you locked up in such a place? It's OK now, this big sister will take care of you!" Under Lisellia's care, Leonis is shocked to see that the world has completely changed. Bewildered and confused, Leonis finds himself enrolling at the Holy Sword Academy.

This one-shot was a short extra in a guide book for a Sirens game. A mysterious siren out at sea drives fishermen to madness.

Aang, the strongest human warrior on the verge of death, has inexplicably travelled 60 years into the past, with the double-edged sword of the “strongest demon” power hidden inside him. “The only way to escape the fate of the pastis to evolve. Aang: “Don’t let yourself be a slave to your limits, break free and become a demon that reigns!

Our main character wakes up and finds himself in another world. But instead of special abilities or weapons, his entire house has been teleported with him. Now follow his journey trying to survive with his new demon neighbors.

The True Heavenly Demon served as the young leader of the Demonic Cult for 100 years because his father, the Cult leader, lived a long life.
However, after inheriting the Cult Leader’s position, which he did not desire, he died after just one year.
But when he woke up, he was now a baby!
He was abandoned on the roadside, but he was picked up by a Taoist from Kunlun, a sect belonging to the justice faction.
That’s when he became Jung Gwang, the youngest pupil of Jung Jabae.
As he died of natural causes, he didn’t have any grudge.
He was more curious about a life with warm relationships among people instead of a bloody one.
He couldn’t enjoy his previous life because he was busy cleaning up his father’s mess, so shouldn’t he live for himself this time?
But he’s now a child. After entering Kunlun, he must at least make sure he won’t have any regret before the final moment.
Under his influence, Kunlun is gradually changing.
Taoism? That’s none of my business.
Demonic way? I’m a little sick of it.
The story of a turbulent life in Murim of the reborn True Heavenly Demon.

Following the untimely passing of his childhood friend and his little sister, Io Haruomi is constantly haunted by their deaths, forever feeling powerless and unable to escape the guilt he feels for letting them die. Despite this, he continues to press forward, attempting to enjoy an ordinary life. He goes to high school, hangs out with his friends, and generally passes himself off as a normal 2nd-year high school student.

One day, however, Haruomi encounters an "Eda", a girl with glowing red eyes and demonic powers. Amidst her escape from the "Seven Great Gospel Organizations", she reveals that he too is an Eda, and the powerlessness he feels is completely unfounded. Before he knows it, Io Haruomi is thrown into the middle of a battle between man and devil.

And as his eyes too begin to glow red, the side he is on is no longer so clear.

In the year 2050 AD, Humans live in a world filled with science and electronics, but the "Demon Capital" Shanghai has never been rid of demons. Fortunately, the supernatural Demon Taoists Corporation is here to ensure that neither vampires, demigods, or even trans-cultural literary icons trouble the citizens...at least, for too long.

Monsters have long threatened humanity’s existence. To fight against these beings, Keith, the youngest person to ever become a sage, joins a knight order and shows immense success on the battlefield. However, that doesn’t last long, as a quarrel with an incompetent higher-up gets him fired from the order. With nowhere to go, Keith is assigned as a teacher, and with his talent for bringing out the best in his students, his class is about to reach unbelievable heights...