By the 2040s, technology has advanced to the point where Professor Junichirou Yamano is able to build mini-robots possessing massive destructive power. He names them Little Battlers eXperience (LBX), and he believes that they will one day change the world. But Yamano's fate proves cruel, as the plane carrying him and his fellow designers vanishes above the Pacific Ocean, never to be seen again.
Years later, the invention of extremely durable cardboard inspires the production of small-scale scenic battlefields. Within these miniature arenas, kids remotely control their LBXs, engaging in exciting combat showdowns. Professor Yamano's son, Ban, shares his father's passion for LBX, but his mother forbids him to get one. However, that changes when an injured woman in a lab coat hands him a mysterious suitcase before fleeing from her pursuers. Inside the case is LBX AX-00, a unique model that becomes Ban's robot partner Achilles—and eventually humanity's last hope.