In a world without music, a young female cyborg uploads music into her body and brings about a revolution.

In a world without music, young Echo was there the day legendary "Player" Jimi Stonefree and his mecha disappeared while fighting the mysterious Earless. Ten years later, he meets an amnesiac young girl named "Mu" who has an input jack on her back. Could she be a "Player" like Jimi? Together they set off on a journey to unravel her past and save humanity.—Crunchyroll

In a world without music, Echo saw Jimi Stonefree disappear fighting the Earless. Years later, he's built his own Equipment that only "Prayers" can pilot such as the amnesiac girl named "Mu". The duo's trek to recover her memories could just save the world.—Hulu

In a post-apocalyptic future that has been torn apart by shadowy creatures known as the Earless, humanity's heroes are the Players, who pilot mecha known as Equipment to battle their inhuman enemies while earning fame and fortune to boot. Echo is a young tech-head who dreams of working amongst the Players and their Equipment, going so far as to build a makeshift mecha of his own, but he has long since resigned himself to life in the destitute scrap-heaps that cover so much of the world, now. That is, until he discovers an amnesiac named "Mu" who has a mechanical port in her back that is the telltale sign of a Player. The pair become fast friends, and they vow to use their skills to fight for the world and defeat The Earless.—Anime News Network