To address Earth's dwindling fossil fuel reserves, the "Quantum Reactor," a novel energy source, was developed in 2031. Regrettably, the equipment malfunctioned and triggered a catastrophic event known as the "Shouryuu Crisis," unleashing unknown forces that decimated the environment. The appearance of "B.R.A.I.," a hybrid being, threatened humanity's existence. Following the ordeal, Leon Lau, a top scientist involved in the "Shouryuu Crisis," settled near the surviving human metropolis, Neo Shouryou. Collaborating with Chloe Lau, his "family contract" partner, they devotedly developed their own tactics to fend off the B.R.A.I. threat after seven years.