As a six year old, Rintaro is diagnosed with Henisei Tashu Ijou Syndrome (also known as Hentai Syndrome), a disease that could kill him if he gets sexually aroused. To save him and provide a way for him to live as normal a life as possible, his father teaches him the ways to control his body and mind for ten years in the mountains, with the martial art of the Koei Sougetsu. When he's 16 he chooses to enroll Nangokuren High School, which he assumed to be the biggest all-boys school in the country but is actually the biggest all-girls school that has just gone coed.

On his first day he stumbles upon a large scale battle and learns that the first rule of the school is that it "Abides the Law of Nature" which has turned the campus into a war zone-like environment. Rintaro now sees transferring out as his mission, but will it be that easy now that he's caught the eye of the 3 "Dragons", the bodacious female leaders of the three biggest factions around?

From JanimeS:

The world of Siesta is set in fantasy Europe where there are people called bullet users who were discriminated against badly for reasons unknown to readers as of volume 1.
The discrimination has gotten much weaker due to Grande Corp's efforts to wipe out the decades-old pirate faction with the help of Bulletron, a battle suit designed exclusively for bullet users.

The story begins as the protagonist Dia Canto tells you a little bit about herself: how she became an orphan, how she met her foster family, and how she is very much in love with her step brother, Loe. However, her affection toward Loe is brutally crushed before it would even bear fruit and she goes out to vent her sadness. This is when she encounters Cid Leon, who she would ultimately be paid to "protect".

A powerful grand wizard named, “Raim” reappears after a millennium because of a failed experiment. While sets out to regain his lost tower, he meets “are” and “ere” who have been trafficked as slaves... a combination of a weird grand magician who only uses his wits to make money and the cute, lovable brother and sister of the miao tribe! Their endless adventure is beginning to unfold. Editorial staff’s comment Will Raim be able to regain his lost tower?! 

Manhwa you may like:
+ This is another ambitious work of Sung San Young, The Gamer
+ Tower of God
+ The God of High School

Superpowers are now common among the world's population. The manifestation of powers is known as Girls' Witch Syndrome, and the origin of the sudden large scale bestowal of extraordinary abilities to children is an entity named the Mother Witch. Ayumu Takenami carries the title of Brave Star as the top ranking CARD member.

CARD is an organisation formed from the children and girls that have superpowers. After he dispatches armed kidnappers with his bare fists somewhere in the Middle East, Ayumu drops everything to go see his crush in Japan. Yuki Saimiya is an average 17-year-old high school girl with insignificant powers but wishes she could be more like the rumoured Brave Star.

From Easy Going Scans:
Before, magic filled up the world, and then magic suddenly disappeared, from everywhere.
Magicians can’t perform magic anymore, so now these formerly powerful, now talentless ones are looked down upon by warriors and practically everyone else. But two people in the world are able to perform magic after its disappearance, a power-hungry wizard and a young boy who loses everything he holds dear.
Follow Melrose and his companions in their adventures as they try to solve this Dark Air mystery.

The young Erwin Smith is a rising star in the Survey Corps, humanity's only hope of defeating the man-eating monsters known as Titans. Ruthless and dispassionate, Erwin’s mind is devoted to strategies and intrigue. But beneath Erwin’s feet is another world, the Underground, where humans are born and die surrounded by the garbage the Capital throws away. Here, the criminal Levi survives on his wits and agility. But when these two ambitious men cross paths, who will prove himself stronger?
The origin story of Levi and Erwin.

Hida Kizuna possesses the HHG (Heart Hybrid Gear) ability, but it is not strong enough to make him particularly important. His older sister calls him to transfer to a strategic defense school, where many of the students (many of which are large-breasted girls) use their HHG abilities to fight invaders from another world while wearing extremely skimpy pilot outfits. Kizuna's fighting ability doesn't measure up, but his sister has another plan-- apparently having erotic experiences with Kizuna will allow the girls to replenish their energy or power-up. It looks like his new school life is going to be full of embarrassment.

Set during the Goryeo military regime, a hero that arises from a slave to be reborn as a general.

Enma's daughter Batsu is looking for help to take down some demons. And who does she turn to...? Normal teenager Takuan! 

Senou Natsuru is a normal high school boy. One day he wakes up to find himself turned into a girl. A stuffed tiger "Harakiri Tora" comes to life and tells him to fight as a female psychic fighter "Kämpfer". Having no idea about what's going on, Natsuru is involved in the battles against other "Kämpfer".

Kämpfer is German for fighter.

Based on Valkyrie Drive: Bhikkhuni PS Vita game.

Martial artist Min Deul-le finds herself trapped in the body of Dorothy, the magician, and embarks on an adventure in the fantasy world of Ozland.

"A couple of elves, a gnome and an android walk into a bar… Ranial, Thame, Ian and Math, four strangers brought together by circumstance, set off on a series of cybernetic adventures in the wake of a war that has left their world a post-apocalyptic fantasy wasteland. Words by Sam Machado, Art by Cynthia Sousa (Theamat), Colors/Letters by Amanda Sousa Machado, Created by Bradley Mason."

Elf & Warrior follows the adventures of a young, optimistic Elf named Basri and his Uncle Hector, a reformed (sort of) criminal in a unique fantasy setting full of strange monsters and magic.

An Onmyodo School Fantasy of a Failing Private Onmyo Academy Student!!
Tsuchimikado Harutora was born into a prestigious Onmyoji family, but he can't see "spirit energy". Therefore, he's been enjoying a peaceful daily life with his friends at an Onmyo branch school. One day, his childhood friend Tsuchimikado Natsume, heir to the head family, suddenly appears. Will this cause his destiny spring into motion!?

The setting of Devil Survivor 2 spans the whole country of Japan. It tells the story of Japanese high-school students who receive emails from a website foretelling their friend's deaths. Mysterious creatures invade the country, and the students enter a pact, enabling them to summon demons from their cell phones with a special Devil Summoning App.

The plot is a monster who came from the future to change the past. One woman must be removed to change the past. The name of the target to remove is Jung Eunji. In order to approach Eunji who is a hero, Tae-gwu is also a prospective hero. Will Taegu remove the threat and change the future?

With the space program attempting to travel to Mars, 21st century scientists were tasked with warming up the planet so that humans could survive on its surface. They came up with an efficient and cost effective plan of sending cockroaches and mold to the surface so that the mold would absorb the sunlight and the insect corpses would serve as a food source for the mold.
It is now the year 2577 and the first manned ship to Mars has landed on the planet and the six crew members are ready for their mission. But what they find are giant mutated humanoid cockroaches with incredible physical strength. The crew members are easily wiped out, but not before sending a transmission back to Earth. Now, humanity will send elite warriors to exterminate the mutated bugs and claim back Mars.

Note: Was nominated for the 6th Manga Taishou in 2013.