Daybreak strips the TV series down to its core: two siblings walking into a mission to kill a half-demon, not knowing they're about to meet the person who will shatter the order they've always known. The OVA doesn't explain Akihito; it just shows him existing in the space between human and monster, and watches Mitsuki and Hiroomi realize that some lines blur too much to matter. This is the origin story that makes every scene between these three people in the actual series hit harder, because you see the exact moment their world becomes complicated.

Three years before the TV series, Hiroomi Nase sets out on a mission to subdue Akihito Kanbara, a notorious boy who is half human and half youmu. His younger sister Mitsuki is curious about the job and comes along, and the two siblings meet Akihito for the first time. They soon learn that others are searching for Akihito too. This OVA episode zero of Kyoukai no Kanata came bundled with the seventh Blu-ray and DVD volume and blends supernatural action, fantasy and drama.