In a futuristic dystopian world where memories are literally stored, bought and sold and rich have all the privileges, a young amnesiac is trying to find out who he is.

A boy with no name awakens with a hole through his chest, a strange marking on his belly, and no memories. The one link to his past is a locket containing a picture of a girl whose name he does not know. Within moments he meets Popo, who unlike the memory-less boy has a purpose. Through Popo, the boy learns that where he is a body without memory, in this world there are many who are only memories with no body. The rich harvest the choice bodies, leaving only the dregs for those down below. And yet even though he has no memories, there are many who seem to want his life.—Crunchyroll

In a world where memories exist in memory chips separate from the body, death of the body no longer means death of the soul. It is possible for memories to be viewed, altered, and transferred between bodies. These memory chips are used by the rich to obtain eternal lives in carefully selected bodies, while for the poor, selling their own bodies and conserving their souls in the chips often become the only way to earn a living. An electrolytic cloud in the sky serves as a barrier between the heavens of the fortunate and the underworld of the destitute, making this social division impregnable. One day, a man named Kaiba wakes up in an empty room with no memories, a mysterious hole in his chest, and a locket holding the picture of an unknown woman. After escaping an attack and stumbling upon a decrepit village of underworld residents, he begins his adventure across the different planets of this strange universe to find out more about his own identity and the woman he once knew. Through a journey of self-discovery and acceptance, Kaiba weaves together tales of souls and spirits and explores the importance of memories.—MAL Rewrite