In a world where negative energy manifests into monstrous beings, only skilled 'Sweepers' can vanquish them and restore harmony. Kyuutarou Horikita, a seemingly grumpy student at Kurokado High School, hails from a lineage of these special individuals. His encounter with Fumi Nishioka, a homeless transfer student with a hidden talent for combating darkness, leads to her becoming part of his family's Sweeper legacy. As Fumi's powers awaken, a sinister faction sets its sights on exploiting her untapped abilities, setting the stage for a battle of light against darkness.