The story of Kyoukai no Kanata is set in a world where creatures from the spirit world called Youmu (妖夢, lit., "catastrophic dream") roam in the human world under human guises, and trained specialists called Spirit World Warriors (異界士, Ikaishi) protect humans from Youmu attacks.
Akihito Kanbara is a high school student who apparently has a Youmu lineage and a peculiar regenerative ability that exceeds that of a normal human's. In an unexpected encounter, Akihito saves a classmate named Mirai Kuriyama, who was about to jump off the school building. Following this encounter is Akihito's discovery of the world of Youmu and Spirit World Warriors.