Set in a post-apocalyptic world, Rebuild World depicts a society that has endured the aftermath of an unknown catastrophe for several decades. While humanity perseveres, the majority of the population resides in impoverished conditions. In this harsh reality, becoming a hunter is crucial for survival. Hunters venture into the ruins of the "Old World" to scavenge lost technology, all while confronting the menacing creatures that emerged from the collapse of society.

Akira, a street orphan, aspires to become a hunter in order to discover ancient technology and improve his circumstances. However, his initial expedition into the city ruins nearly ends in tragedy. Fortunately, Akira is saved by Alpha, a mysterious artificial intelligence that communicates solely with him through augmented reality. Alpha reveals her desire to explore a treacherous part of the Old World but lacks a physical form to do so. She proposes a mutually beneficial arrangement, where she will serve as Akira's guide and teacher in exchange for his assistance in exploring the ruins. Intrigued, Akira accepts the offer, and thus embarks on a dangerous journey of technology hunting.