While en route to school, Suzume Iwato encounters Souta Munakata, a young man on a mission to explore deserted locations. Intrigued, Suzume guides Souta to a nearby ruin, only to be lured by her own curiosity to follow suit. Inside, she uncovers a mysterious door leading to a fantastical realm she can observe but not enter. When a peculiar stone morphs into a feline being and scampers off at her touch, Suzume, alarmed, departs, unknowingly leaving the door ajar. Little does she know, this oversight triggers a chain of events as the unleashed 'keystone' permits malevolence to traverse into Japan. To mend her misstep, Suzume partners with Souta, who harbors a mission to thwart the spreading darkness by sealing all portals that endanger their homeland.