In the far future, humans abandon a devastated Earth and traveled to outer space. However, due to unknown phenomenon that prevents them from traveling into space, humanity returns to Earth only to find it inhospitable except for Japan. To accommodate the entire human population, pocket dimensions are created around Japan to house in the populace. In order to find a way to return to outer space, the humans began reenacting human history according to the Holy book Testament. But in the year 1413 of the Testament Era, the nations of the pocket dimensions invade and conquer Japan, dividing the territory into feudal fiefdoms and forcing the original inhabitants of Japan to leave. It is now the year 1648 of the Testament Era, the refugees of Japan now live in the city ship Musashi, where it constantly travels around Japan while being watched by the Testament Union, the authority that runs the re-enactment of history. However, rumors of an apocalypse and war begin to spread when the Testament stops revealing what happens next after 1648. Taking advantage of this situation, Toori Aoi, head of Musashi Ariadust Academy's Supreme Federation and President of the student council, leads his fellow classmates to use this opportunity to regain their homeland. (Source: Wikipedia)

Yuuki Oojima is a member of his high school's Food Research Club, whose main activity is eating snacks bought with funds allocated to them by the school. However, this peaceful and wasteful lifestyle is under threat as the upcoming student election draws near. Satsuki Shinonome, a major candidate and the head of the department of financial affairs, campaigns on a platform that includes disbanding meritless clubs such as the Food Research Club and redirecting their budgets to proper ones. Understandably, the Food Research Club is in an uproar over this development, with president Chisato Sumiyoshi vowing to preserve it. But what can they even do to stop the highly competent and popular Satsuki from getting elected? [Written by MAL Rewrite]

The Kodomo No Omocha OVA is a thirty-minute animation video that was made before the TV series. It covers the first volume of the manga, so it's equivalent to TV episodes 1-6. It relates Sana's troubles with Hayama at school as a result of the "oyakodon baka" situation and culminates when Hayama's dad and sister realize their mistakes thanks to Sana's efforts.

As the sole survivor from a squad that was sacrificed and hung out as scapegoats for embezzlement of military resources at the end of the 100 years war, Mellowlink Arity is out for revenge. Carrying the dogtags of his deceased comrades and armed with a dated anti AT rifle, he swears to hunt down and exact revenge on the corrupt officers that betrayed his squad, and maybe even uncover the truth behind the plot as well.