Kyoukai no Kanata:Beyond the Boundary Shinonome prequel

The pilot episode of Kyoukai no Kanata takes place three years before the TV show and showcases the efforts of Hiroomi Nase to defeat Akihito Kanbara, a prominent figure in the universe as a half-human, half-youmu. Hiroomi's sister, Mitsuki, is intrigued by the task and becomes involved as they cross paths with Akihito for the very first time. As events transpire, they discover that there are others interested in facing Akihito, leading to the origins of the Kyoukai no Kanata story.