The story takes place on Earth nearly a thousand years in the future. Following a great war between artificial intelligence and humanity, monsters known as "Tai Sui" roam the land, drastically altering the natural environment and societal structures. Humans invented a series of new technologies related to "BOX"—boxes—and, using these boxes as partners, fiercely resisted their enemies. The elite individuals capable of "resonating" with their box partners are called Box Masters. Rokuma, a previously overlooked and unremarkable Box Master, is chosen by the little dinosaur box "Theo" to begin a mission to protect the city-state...