Over three hundred years have passed since the Calamity War, the great conflict between Earth and its outer space colonies. Now Earth is ruled over by four economic blocs, and the military organization Gjallarhorn is responsible for keeping the peace. Mars, on the other hand, depends heavily on Earth's economy. Horrified by the appalling living conditions that Mars' inhabitants have to bear, Kudelia Aina Bernstein, a young aristocrat from the Chryse Autonomous Region, gets involved in the Red Planet's independence movement. She hires the services of a local company, Chryse Guard Security (CGS), to escort her on the journey to Earth to negotiate economic conditions with the earthly bloc that controls the region. The Third Army Division—consisting of Mikazuki Augus, Orga Itsuka, and many other child soldiers—are chosen to protect her. When Gjallarhorn attacks the CGS facilities to assassinate the young revolutionary threatening their interests, Orga and his comrades must not let the attackers accomplish their goal—in fact, Gjallarhorn's actions might turn out to be the unintentional catalyst that leads the children to be the forgers of their own destiny. [Written by MAL Rewrite]

"To be quiet and do as you're told, that's the cowardly choice." These are the words of Junk Dog, an underground fighter of Megalo Box, an evolution of boxing that utilizes mechanical limbs known as Gear to enhance the speed and power of its users. Despite the young man's brimming potential as a boxer, the illegal nature of his participation forces him to make a living off of throwing matches as dictated by his boss Gansaku Nanbu. However, this all changes when the Megalo Box champion Yuuri enters his shabby ring under the guise of just another challenger. Taken out in a single round, Junk Dog is left with a challenge: "If you're serious about fighting me again, then fight your way up to me and my ring." Filled with overwhelming excitement and backed by the criminal syndicate responsible for his thrown matches, Junk Dog enters Megalonia: a world-spanning tournament that will decide the strongest Megalo Boxer of them all. Having no name of his own, he takes on the moniker of "Joe" as he begins his climb from the very bottom of the ranked list of fighters. With only three months left to qualify, Joe must face off against opponents the likes of which he has never fought in order to meet the challenge of his rival. [Written by MAL Rewrite]

Vesper is a secret agency fighting an army of alien invaders by using super-powerful battle androids. Mahoro is Vesper's most powerful battle android and has won many battles, but she has little operating time left and soon will cease to function. However, if she lays down her arms and conserves her remaining power, the time she has left can be prolonged to just over a year. Mahoro is given an opportunity to live the remaining time she has as a normal human. She chooses to live as a maid for Suguru, a phenomenally messy middle school student who lives by himself after his family passed away. (Source: ANN)

As the relationship between Mahoro, Suguru and his classmates develops further, another android girl enters their lives and becomes attached to Mahoro. All the while, the number of days before Mahoro is to shut down decreases steadily. (Source: ANN)