Maiku Kamishiro's past has always been somewhat of a mystery to him. The only clue he has to who his family might be is an old photograph showing two young children, a boy and a girl, playing in a small pool outside of a blue house. In an attempt to find his family, he moves to this blue house and begins working as a programmer. He's living a comfortable life until the day two very different girls show up at his door, both in possession of the same photograph, and both claiming to be his twin. With no way to prove who is a relative and who is a stranger, Maiku allows both girls to move in with him until they know for sure. 

(Source: ANN)

In a dystopian future where Japan's political organization has crumbled after the Great Tokyo War, Japan is broken up into 10 independent nations, with each nation controlled by a gang led by a "Best," a human-proclaimed prophet with destructive superpowers. Nozomi Moritomo is a "Rest"—a normal girl that has just started out as a rookie in the local gang. She wants to help the Best Masami Utoku, her childhood friend and role model, in the ongoing territorial dispute. When Masami becomes severely injured and unable to fight, Nozomi decides to go on a mission to complete the requests sent to Masami from all over Japan. Along the way, she meets Yukina Kosaka, a shy girl with no sense of direction; Ai Hibiki, an upbeat girl who loves eating; and Chiaya Misono, a quiet and mysterious girl that wears a gas mask. Together, the four girls travel all over the country on their motorcycles while getting involved in territorial wars, disagreements, and even suspicious conspiracies. [Written by MAL Rewrite]

After the climactic battle to decide the fate of humanity, the hero Max, alongside his party, emerges victorious against the formidable Demon Lord. As he draws his last breath, the defeated Maou vows to return more powerful than ever to take his revenge. Ten years later, although Maou has resurrected, the process is incomplete, resulting in him taking on the form of a child. Nevertheless, not wanting to waste another second, Maou pays his nemesis a visit—but the hero who once gallantly protected humankind from the demon's clutches is now a pitiful slob bearing no resemblance to a man of his former caliber. Despite his disappointment, Maou moves in with Max in hope of building him back up into a worthy adversary. But as the demon learns more about the events that transpired in the decade of his absence, he realizes that there is a story behind Max's downfall that he knows nothing of.

Short episodes aired on KyoAni's official YouTube channel.