The story is set in a distant future where Japan is divided into feudal territories and conquered by other countries. There is a floating city named Musashi that is composed of eight ships in the skies. A war that will determine the fate of the world will be fought by students on the Musashi.
In the far future, humans abandon the devastated Earth and move to the upper world "Tenjou." But Tenjou and the law of causation collapse due to a war and humans are forced to return to the Earth, which has turned into an inhabitable planet except for Shinshuu area in the Fat East. Shinshuu is too small to accommodate all the humans, so they duplicate the area and create "Juusou Sekai" in a parallel world. In order to rebuild Tenjou and the law of causation, the returned humans start reproduction of the history from B.C. 10,000. When the reproduction proceeds to A.D. 1413, a war breaks out in Shinshuu and Juusou Sekai falls onto the original world. The humans living in Juusou Sekai lose their land and invade the original world. People in Shinshuu surrender and the land is divided by the invaders from Juusou Sekai. They try to resume the history reproduction from A.D.1457, but the update of the history terminates in A.D.1648. A rumor of apocalypse begins to spread the world.
There's a certain kind of joy that only comes from exploring and experiencing new things. Whether it comes from playing an immersive video game or reading an engrossing book, or perhaps even traveling and finding new things yourself, that feeling is truly unmistakable. From the first volume, Kyoukai Senjou no Horizon manages to elicit that very feeling, to the extent where not even the piles of brick-sized volumes can satisfy my craving for more. Despite being a story about a looming apocalypse, it creates a world you can't help but want to live forever in.
Like its (very, very distant) prequel Owari no Chronicle, and
a lot of other series by its author Minoru Kawakami, Kyoukai Senjou no Horizon places itself somewhere in the borderlands of sci-fi and fantasy. The setting, where renaissance era technology has been reinterpreted to fit in a future in which “ether”, a mystical substance that is part of all things, can be used to sail ships through the sky and much more, is an almost surreal patchwork of elements from the two genres. It simultaneously brings to mind epic high fantasy stories and silly mecha anime. While this synthesis makes it feel cringeworthy and almost bizarre at times, it's also one of the things that sets the series apart from many others.
While on the topic of the setting, it might be worth to mention that anyone getting into the series expecting a fun new perspective on the 30 Years War and the Warring states period will not be disappointed. While an original story on its own, the plot and setting of Horizon is closely tied to these periods of history, with lots of tidbits and fanservice for history enthusiasts.
Storywise, Kyoukai Senjou no Horizon is a tale of a rebellious adventure, a quest to regain the sovereignty of an oppressed country while restoring the emotions of its princess and averting an impending apocalypse. I won't go into depth as to what all that entails - that's what synopses and actually-reading-the-damn-books is for - but I can ensure anyone who has yet to start reading it that it contains everything from fast paced fights, to in depth negotiations on politics and finance, while taking the characters through glorious victories and crushing defeats. On top of that, it contains several heartfelt love stories, beautifully woven into the general plot. It is not all hotblooded action and romance, however. Between the more fast-paced moments, the story takes the time to shine its light on the more serious sides of its characters, at some times giving solemn backstories to explain the actions of its characters, at others having characters have honest conversations about their feelings.
Humor is another integral part of the series, which most of the times is derived from interactions between characters. And boy, I'd be lying if I said some of these interactions didn't actually make me laugh out loud at times. The shameless banter between classmates and the sillier sides of international politics bring lots of fun to the series. Though generally lowbrow and with loads of obscure references to Japanese pop culture, I doubt anyone could read through it without finding themselves chuckling at at least one joke.
While on the topic of jokes, there's one important misunderstanding about the series that needs to be cleared out: that it's entirely about out of big breasted girls doing fanservicey things. While there's definitively a lot of that, it is by no means the main focus of the series. The distinction between “porn with a plot” and “a plot with porn” is important here. The fanservice isn't exclusive to the bustier characters either, so even those who prefer smaller breasts are bound to get something out of it. But when all is said and done the one spending the most time naked out of the cast is a male, and coincidentally the main protagonist of the series.
Regarding the characters themselves, Kyoukai Senjou no Horizon has all the strengths and weaknesses of an ensemble cast. While the main focus lies on the incompetent chancellor Toori Aoi and the mysterious automaton “p-01s”, the story follows multiple viewpoints, letting us experience the events through the eyes of the diverse set of protagonists as well as the villains. This, when coupled with the massive size of the cast, is a big part of what gives the series’ volumes their extraordinary length. But even with those extra pages, not every character can be given an arc and a backstory, making some characters feel underdeveloped in comparison to others, even in the class made up of the protagonists. It is however worth noting that the series hasn't ended yet, and that even the more overlooked parts of the cast might get their time to shine.
The artistic highlights of the series lie in the varied and interesting designs of the characters, and the characteristic uniforms and styles of each nation in the Divine States. From the restrained black, white and red uniforms of the Far East to the Arabic inspired garbs of P.A. Oda, the representatives of each nation are all immediately discernible just from their clothes, even when they have modified it to suit their own style. One of the more disappointing aspects of the art, however, is the artist's apparent reluctance towards drawing mechanical constructions and non-human creatures. Instead, most illustrations feature only humans, with many being reserved for depictions of fanservice.
My advice for anyone who has made it this far into the review is to start reading it at once. Although it can be quite a lot to take in at first, you'll quickly find yourself brought into a whole new world, with lots to experience. The daunting length of the series will eventually turn into a relief that you won't run out of things to read any time soon. Take it easy, read it one volume at the time, and let yourself get lost in the world. If you're anything like me, you'll enjoy every page along that journey.
All in all, Kyoukai Senjou no Horizon is an interesting and original series, that appeals to lovers of adventures, fighting, fanservice, negotiations, romances, humor, history, and much, much more. The plot is intertwined with a complex and intriguing setting, and delivers hotblooded action along with meaningful character development for most characters. Above all, it presents a world you can get engrossed in, and continuously gives you a feeling that there's more to be discovered. If that's the kind of joy you are looking for, this series is definitely for you.