However, these mid-bosses kept getting defeated by the heroes, who continued to grow stronger with time. Which led to the demon king’s army needing to produce even stronger mid-bosses.
It was at that time that a certain demon stepped up.
Demonstrating great wit, she became the demon world’s founder of the official mid-boss training academy!

This is the story of a village where a deity is--on the day of the village festival, the deity endows a boy, Mao, with a destiny. That destiny is to live as a girl. In a small village where forests, lakes, fields, fish, insects, and flowers flourish, Mao, his sister, and his friend confront fate.

Andou is a high schooler who possesses the ability to force others to vocalize his thoughts - an ability similar to ventriloquism. Inukai is young man shrouded in mystery who commands the vigilante group, Grass Hopper, which appeared in a city shaken by the downtown restoration program. This is a tale of courage, resolution… and confrontation; this is a depiction of the two boys’ encounter."Even if it’s nonsense, if you believe in yourself and face things head on, the world will change."This was dropped by Endless Abyss.Though it has 10 volumes (Completed) in Japan.

A small inn just outside of town, hotel new oh dog, a place where adventurers come to rest their tired bodies. The inn owner's fur is as wonderful and fluffy as always. Lilith the inn's poster girl wants to go to school and look for treasure in dungeons?
A new fluffy inn comedy by Kai Yoshino starts now!

Yuuto is an ordinary high school boy who, one day, notices a mysterious tarot card by his bed. He shows it to his parents, who give him the good news - as the son of demonkin, he is eligible to become the next Demon Lord. As such, Yuuto is soon brought to a demonic academy in order to improve his devilish skills and earn the title of demon lord. And, you know, get a harem along the way.

From the author of Masou Gakuen HxH and Ecstas Online.

“Maou Army’s strongest magician” I’m called. Ike, a demon capable of capturing a fort alone. Clearing away enemies with immense magic, he is without a doubt a monster awed by friend and foe. However, he has a secret he can’t tell other demons. “I, actually I’m human you know.” Using modern knowledge to keep his secret, he became treated as a great commander and the driving force of the Maou’s army.

If you had to defeat frightening "Great Demon King" in a fierce fight...
12 cute "Small Demon Kings" have been born again!!!
The Male hero youth, Byron, has been appointed by God to raise the Devil Brothers in order to bring peace to the world.
The hard fight of chores and raising!

In the Maou Lover series:
From Fujoshi Bitches :
V.1 - Maou Lover
“Don’t show that face to anyone else except me”
Mao, the demon-king-like genius pro tennis player, and Hikaru, the S (sadist) and intellectual player, are rivals from when they were juniors!….. It was supposed to be like that but he always looks at me whether it’s during the game or not. Furthermore, suddenly asking me to go out on a date and even French-kiss me…! I can’t stop my heart from beating fast, could this be..... love !?

V.2 - Maou Lover VS Ouji-sama
“You’re not so honest, huh. Even though your body is “honest” like this ❤
”Mao is the devil-king-like genius who hates to lose. His childhood friend as well as his rival in tennis is Hikaru, an intellectual noble-like and a S (sadist) type! Their relationship is like cat and dog because of their opposite personalities. However, they became lovers because Hikaru found out the weak points on Mao’s body. But then, the night at the summer training camp, just when Hikaru was about to attacking Mao but he suddenly stopped... Because i’m the king so just come and do me ❤ I will never say it!!

A lonely "demon lord" and a self-centered "hero"!?

What about "villager A," caught in the middle!?

This is a school that prepares people for roles in fantasy stories. However, those who possess the "traits" of a "warrior" or "wizard" are but a few. Most will become no more than mere "villagers." I, Satou, am also one of those "villagers"; but one day, a girl possessing the trait of "demon lord," Ryuugamine Ouko, set her eyes on me. She's short and a surprisingly calm, good girl, but she'll abruptly mutter about destroying mankind; give me a break. Taking up the opposition with passion is my childhood friend, Hikarigaoka Tsubasa; she's more trouble. This girl is also quite the beauty, but as soon as she makes up her mind, she's an absolute troublemaker...

This is a world that's slightly abnormal, with a slightly abnormal cast, interwoven in their dilemmas; a slapstick comedy!

From MangaHelpers:
Kusumi Chiharu gets a message one day that he has been selected as a Monster Tamer, and he is prompted to select his first partner. He thinks little of the message until he receives a giant package the following day. He assumes it's the porn books he ordered, but the huge box ends up containing the unconscious body of a mostly naked girl! She's a ghoul named Zonmi, who intends to fight with him as his partner. However, it turns out that other hot girls at his mostly-male high school are also magical creatures, and Zonmi may not be the only one who wants to fight by his side.

Before I realized, I had become the guardian of a dungeon, a Demon Lord. I was suddenly in a dangerous world with giant monsters loitering around, fighting for their existence, so I thought to go about developing the dungeon in order to not die but —- for some reason I was having quite the good time…. How did it turn out like this?

The protagonist, Yuki, having to live in that world now, uses his bold and sharp senses and spends time with a supreme dragon girl and a vampire girl; Sometimes laughing, sometimes being angry, passing days doing what he likes.

"I do not trust humans. They’ll betray you without fail.” Aur, the man who had obtained the ability and right to become the Maou at the end of his life of research. Summoning the succubus Lilu, he then sets out on creating his own domain, a gigantic labyrinthine dungeon… The misanthropic Maou taking on the world, the curtain rises on a dark harem fantasy!

The Demon King has finally awoken. For the purpose of conquering the world, he decides to first kidnap some human. By the way, the one he was searching for was a stupidly capable "Secretary"...!
She does her work promptly and with unimaginable skill. Because of her, humanity is heading toward danger at Mach speed!!

Iguel sama the demon who soon will become the greatest member of the Demon King Army's Four Heavenly Kings!

Except that on the day she thought she would finally be promoted she instead get transferred to the Demon Resources Department which seems to be the subject of lots of suspicious and scary rumors...

An oneshot by Yoshikawa Miki; a teacher for the fifth graders claims to be the king of the underworld!? Some of the students then decides to investigate him, is he really from hell?

For a long time, humans were living in fear of the Demon Lord’s dreadful menace.

However, at long last, a hero, who could successfully draw out the holy blade emerged and defeated the Demon Lord. Finally, the world will go back to its peaceful state once again…

Or so everyone thought.

Office Lady falls from a building is reincarnated into another world and ends up at the Devil Kings castle. Can she save him from the bad ending?

Zagan is feared as an evil mage, he is awkward and has a sharp tongue, and once again had to put down thieves that encroached on his territory when he researching that morning. In a dark auction, he finds a white slave elf, Nephie, who holds a peerless beauty. Falling in love with her at first sight, he uses his fortune to buy her, but as poor as he is socially, doesn't understand how to connect with her. Thus, the clumsy cohabitation of the mage that can't convey his love, and the slave that pines for her master but doesn't understand how to bring it up, begins.