Kyoukai Senjou no Horizon is composed of twenty-six episodes split into two broadcast schedules, with the first thirteen episodes released from October 2 to December 25, 2011. The series continued into its second season, entitled Kyoukai Senjou no Horizon II, on July 2012.
Kyoukai Senjou no Horizon chronicles the story of a futuristic civilization which returned to Earth after constant warfare hindered them from traveling beyond the post-Apocalyptic Earth. At this stage, a small archipelago called the Divine States were the only hospitable land on Earth. In order to regain the space-faring technology they had lost after many years of war, they decided to recreate history with a book called the Testament as a guide.
It is the year 1648 in the Testament Era. Toori Aoi, Chancellor and Student Council President of the only academy on the airborne city-ship Musashi, faces the ten-year anniversary of the death of his childhood friend Horizon Ariadust in an accident. As he prepares to celebrate the occasion by proposing to P-01s (an automaton who looks exactly like Horizon) he discovers that his suspicion about P-01s' appearance actually has a basis in truth; P-01s is in fact Horizon Ariadust, reborn into a robotic body. In addition to this, Horizon's emotions have been stripped away and are now stored in eight powerful weapons called the Mortal Sin Armaments; which are now in the possession of key people in various established countries in the Divine States.
To retrieve the emotions of Horizon Ariadust, Toori Aoi along with his friends and allies begins a crusade against different obstacles as key events in history are recreated in a futuristic manner.
After retrieving their first Mortal Sin Armament (the Lype Katathlipse), Toori and P-01s travel with Musashi to England where they are caught up in a historical recreation of a key event in the Anglo-Spanish War. The representatives of Tres España and England force Toori and his friends into taking one of the two sides of the war. As the two sides clash, a darker side of the Testament is revealed as an innocent girl is sentenced to die under the orders of the Testament.
Tenzou Crossunite, one of Toori's allies, decides to defy the Testament by saving the girl from her undeserved death; while England's Mortal Sin Armament becomes a valuable target as well.
- Episode 01: Those Lined Up Before the Horizon
- Episode 02: Innocents at the Table
- Episode 03: Commandos in Town
- Episode 04: Covert Ops Under the Night Sky
- Episode 05: Graduates Under the Moon
- Episode 06: Advocate at the Confession Grounds
- Episode 07: Musashi's Knights
- Episode 08: Ruler of the Land
- Episode 09: The Summit's Flower
- Episode 10: The Trumpeter at the Start Line
- Episode 11: Musashi's Mr. Impossible
- Episode 12: Opposition Against Crossing Over the Parallel Lines
- Episode 13: Those Lined Up Above the Horizon
- Episode 01: Members of the Vermillion Grounds
- Episode 02: Herald on the Stage
- Episode 03: Those Descending to the Surface
- Episode 04: Ruler of the Theatre
- Episode 05: The Hunting Ground's Humanitarians
- Episode 06: The Man & Woman in the Plaza
- Episode 07: Storyteller in the Hall
- Episode 08: The Decision Maker on High
- Episode 09: One Parting Under the Night Sky
- Episode 10: Howler at the Theatre
- Episode 11: Successful Candidate in the Flower Garden
- Episode 12: Where the One Scarred by Swords Belongs
- Episode 13: The Greedy Ones Who Cross Borders
The opening theme song of the first season is entitled "Terminated", sung by Minori Chihara, who also voices P-01s in the anime series. Meanwhile, the series has two closing theme songs, dubbed as "Side Horizon" and "Side Ariadust". The "Side Horizon" closing theme song is "Stardust Melodia", sung by Ceui, while the "Side Ariadust" one is "Pieces", performed by Airi.
For the second season, the opening theme is entitled "ZONE / / ALONE", also sung by Minori Chihara. There are two closing theme songs following the format of the first season. This time, however, the songs are dubbed "Side SunRise" and "Side SunSet". The "Side SunRise" closing theme song is "Sora no Uta" by Masami Okui, and the "Side SunSet" one is "Kanashimi wa Dare no Negai Demo Nai" by Aira Yuki.
- Anime Series Official Website (Japanese)