In the distant future, a majority of humans have left the Earth, and the Galactic Alliance of Humanity is founded to guide exploration and ensure the prosperity of mankind. However, a significant threat arises in the form of strange creatures called Hideauze, resulting in an interstellar war to prevent humanity's extinction. Armed with Chamber, an autonomous robot, 16-year-old lieutenant Ledo of the Galactic Alliance joins the battle against the monsters. In an unfortunate turn of events, Ledo loses control during the battle and is cast out to the far reaches of space, crash-landing on a waterlogged Earth. On the blue planet, Gargantia—a large fleet of scavenger ships—comes across Chamber and retrieves it from the ocean, thinking they have salvaged something of value. Mistaking their actions for hostility, Ledo sneaks aboard and takes a young messenger girl named Amy hostage, only to realize that the residents of Gargantia are not as dangerous as he had believed. Faced with uncertainty, and unable to communicate with his comrades in space, Ledo attempts to get his bearings and acclimate to a new lifestyle. But his peaceful days are about to be short-lived, as there is more to this ocean-covered planet than meets the eye.

Nanba is the world's most formidable prison, built to incarcerate criminals who are too slippery to stay in ordinary confinement. The four inmates who occupy Cell 13 are particularly cunning on that behalf, having escaped every other prison with a perfect success rate. There is Juugo, a specialist in locks who has spent the majority of his life in prison; Uno, a gambler with great intuition; Nico, an otaku whose body reacts strangely to drugs; and Rock, a bruiser with a love for food. The daily shenanigans of the four prisoners always cause trouble for the building supervisor, Hajime Sugoroku, who desperately tries to prevent them from breaking out of Nanba. Nanbaka follows the comedic, sparkle-filled exploits of these prisoners and their guards. From three square meals a day to sports festivals, prison life in Nanba isn't actually that bad—and it is the closest these four have to a home. [Written by MAL Rewrite]

Even after spending a considerable amount of time with Takagi, Nishikata is still struggling to find a perfect plan to defeat the expert teaser. A battle of wits, a contest of physical prowess, a test of courage—any strategy he employs to expose her weaknesses is to no avail. On the contrary, Nishikata's pitiful attempts only reveal more of his own flaws, which Takagi takes advantage of to become increasingly daring in her teasing attempts. To make things worse for Nishikata, rumors about him and Takagi may have spread in class due to the frequent interactions between them. However, the optimistic Nishikata believes that wisdom comes with age and that as the days go by, his experience with her constant teasing will eventually bear fruit, leading him to the awaited moment of victory. Thus, Nishikata continues to strive for the seemingly impossible—to outsmart Takagi and make her blush with embarrassment. [Written by MAL Rewrite]

The 150-year-long stalemate between the two interstellar superpowers, the Galactic Empire and the Free Planets Alliance, comes to an end when a new generation of leaders arises: the idealistic military genius Reinhard von Lohengramm, and the FPA's reserved historian, Yang Wenli. While Reinhard climbs the ranks of the Empire with the aid of his childhood friend, Siegfried Kircheis, he must fight not only the war, but also the remnants of the crumbling Goldenbaum Dynasty in order to free his sister from the Kaiser and unify humanity under one genuine ruler. Meanwhile, on the other side of the galaxy, Yang—a strong supporter of democratic ideals—has to stand firm in his beliefs, despite the struggles of the FPA, and show his pupil, Julian Mintz, that autocracy is not the solution. As ideologies clash amidst the war's many casualties, the two strategic masterminds must ask themselves what the real reason behind their battle is. [Written by MAL Rewrite]