鳥居なごむによる日本のライトノベル。イラストは鴨居知世が手掛けている。 KAエスマ文庫より刊行された。「異界士」と呼ばれる特殊な能力を有する存在が、「妖夢」と呼ばれる人間に害を及ぼす存在と戦うダークファンタジー作品。第2回京都アニメーション大賞奨励賞受賞作。 ある日、神原秋人は今にも校舎の屋上から飛び降りそうな栗山未来を見つける。それぞれに事情を持つ半妖夢の少年と血に纏わる異界士の少女が出会い、やがて2人は大地主である名瀬家を巻き込んだ事件に関わっていく。
The story is a recap of the TV series "Kyoukai no Kanata". Mirai Kuriyama is the sole survivor of a clan of Spirit World warriors with the power to employ their blood as weapons. As such, Mirai is tasked with hunting down and killing "youmu"—creatures said to be the manifestation of negative human emotions. One day, while deep in thought on the school roof, Mirai comes across Akihito Kanbara, a rare half-breed of youmu in human form. In a panicked state, she plunges her blood saber into him only to realize that he's an immortal being. From then on, the two form an impromptu friendship that revolves around Mirai constantly trying to kill Akihito, in an effort to boost her own wavering confidence as a Spirit World warrior. Eventually, Akihito also manages to convince her to join the Literary Club, which houses two other powerful Spirit World warriors, Hiroomi and Mitsuki Nase. As the group's bond strengthens, however, so does the tenacity of the youmu around them. Their misadventures will soon turn into a fight for survival as the inevitable release of the most powerful youmu, Beyond the Boundary, approaches.
