Three years ago, the world learned that harpies, centaurs, catgirls, and all manners of fabulous creatures are not merely fiction; they are flesh and blood - not to mention scale, feather, horn, and fang. Thanks to the "Cultural Exchange Between Species Act," these once-mythical creatures have assimilated into society, or at least, they're trying. When a hapless human teenager named Kurusu Kimihito is inducted as a "volunteer" into the government exchange program, his world is turned upside down. A snake-like lamia named Miia comes to live with him, and it is Kurusu's job to take care of her and make sure she integrates into his everyday life.
Five years ago, while battling an alien force known as the "Mimesis," Dannar pilot Goh Saruwatari first met Anna Aoi. Today, on the day of their wedding, the ceremony is interrupted when the Mimesis strike again. As Goh struggles in his battle against the alien threat, Anna stumbles upon a top secret robot known as the "Neo-Okusaer" and uses it as a last-resort to save her fiancee. At that moment, Dannar and Neo-Okusaer merge to become the mighty robot "Godannar."
The story follows Issei Hyōdō, a dim-witted, lecherous second-year high school student who is killed by a girl on his first date ever. Issei is reincarnated as a devil, and from that day forward, he serves as an underling of Riasu, a high-level devil who is also the prettiest girl on Issei's campus.
Takeru Ohyama, a young normal yet perverted minded guy, got accepted and now goes to a school that, unknown to him, was where combat and magic is used. On the first day, he meets again after three years: Haruko Amaya, his childhood friend, Inaho Kushiya, a girl who says she's his fiance, and Kodama Himegami, a blonde who wants to kill him. Finding out that there are many girls there that just don't like him, he is told that everyone there uses a special magic ability while using an item or weapon called a Maken. Later, he finds that no Maken is acceptable for him and doesn't know what to do, since in this school the students get into duels that showcase their magic and combat power, of which he seemingly has none.
Takeru continues his education at Tenbi Academy as part of the newly formed Security Committee. As a team with the other members they battle unscrupulous individuals who use their Maken for evil purposes. In the meantime, his libido and the conflicting romantic interests of the girls surrounding him complicate matters considerably.
Nine idiosyncratic individuals are linked by the "Chōjō Kagaku Kirikiri Basara" occult summary blog run by 17-year-old second-year high school student Yūta Gamon. Little incongruities that occur around these nine eventually lead to a larger, unimaginable event that may alter what is considered common sense in this world.
In the city of Gainos, Reina the vagrant warrior enters the competition of Queen's Blade to decide the new queen of the continent, but there are a number of obstacles in her way, each with their own reason for fighting.
In four years' time the competition that will decide who the next Queen shall be will start. The strongest warrior will continue to rule the country according to tradition and expand it. The contestants need only be older than 12 years. They need not be human, intelligent or even of that country. The rules for the tournament are simple: murder is allowed. Any weapon can be chosen. The winner is decided when one of the participants flees or can't move anymore. The event is broadcast by the court's magic teacher through a crystal sphere to the whole population to see and enjoy.