30 years ago, a disaster known as a spacequake obliterated the center of Eurasia without warning, leaving 150 million corpses in its wake. Ever since that day, mankind has lived in constant fear of the spontaneously recurring spacequakes. One day, an ordinary high school boy named Shido Itsuka discovers a mysterious girl at ground zero of a recent spacequake. Shido learns, through the help of his sister Kotori, that the girl is one of the Spirits: mystical creatures responsible for the genesis of the spacequakes. As captain of the anti-Spirit airship Ratatoskr, Kotori recruits Shido to help "seal" the spirits, thus ending their threat to mankind. There's just one catch: the only way to seal a spirit - is to make her fall in love with you.