April 10.The series begins with a spatial quake devastating the center of Eurasia. Thirty years have passed since the spatial quake, and the ditzy Kotori Itsuka and her adopted older brother Shidō live in Tengū City, Japan. For the opening ceremony, Kotori and Shido make a promise to meet at a diner later that day. As school ends for Shido, a spatial quake alarm sounds throughout the city for the citizens to enter shelter areas immediately. After being unable to contact his sister, Shido uses his GPS to confirm that she is still within the city according to their promise. He leaves the shelter to find her and in doing so, is outside when the spatial quake occurs and creates a giant crater, thus meeting a spirit-armor girl in the center. After a battle between the Spirit and the AST unit; those eradicate Spirits, where Shido witness his popular classmate Origami Tobiichi is a part of the AST, he meets the Ratatoskr organization on their airship, the Fraxinus, with serious Kotori the commander, and learn about the Spirits. He gets knowledge of his ability that can seal away Spirits' powers by making them fall in love with him.