Thirty years ago a strange phenomenon called a "spacequake" devastated the center of Eurasia, claiming the lives of at least 150 million people. Since then, smaller spacequakes plague the world on an irregular basis. Shido Itsuka, a seemingly ordinary high schooler comes across a mysterious girl at the ground zero of a spacequake and learns from his sister Kotori she is one of the "Spirits" who are the real cause of the spacequakes that occur when they manifest themselves in the world. He also learns that Kotori is the commander of the airship Fraxinus, crewed by the organization Ratatoskr, and is recruited to make use of his mysterious ability to seal the Spirits' powers thus stopping them from being a threat to mankind. However, there is a catch: to seal a Spirit's power, he must make her fall in love with him and kiss him.
Infinite Stratos (IS), a weaponized exoskeleton system, has become the dominant tool of warfare and conflict. Unfortunately for the men in society, only women are able to operate Infinite Stratos…with very few exceptions. One of those exceptions is Ichika Orimura, an orphan raised by his older sister, who is herself a famous IS pilot. When his compatibility with Infinite Stratos is discovered after he accidentally touches one at the age of 15, he is given a scholarship and enrolled in a school that specializes in training IS pilots. Which means an interesting life surrounded by girls for this shy, unassuming boy.
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.