When they manifest, spirits—powerful beings from another world—can cause spatial tremors. One approach to deal with them is to kill them with force, or to make them fall in love and seal their abilities. After sealing three Spirits, Shidou Itsuka works with Ratatoskr to find additional Spirits and date them in order to protect the world from further calamity. But this time, a more powerful menace appears to have become aware of their operations, so their troubles won't be restricted to Spirits this time.