Jean Grey and Sarah Grey are mutant sisters. However, the elder sister, Sarah Grey, was kidnapped and experimented on by the DODC, an organization seeking to replicate and exploit the powers of superhumans. On the surface, the DODC is a government agency dedicated to human safety and risk management. In reality, they are a powerful group that employs the Hand, a dark ninja clan, as their paramilitary force, while researching and weaponizing alien technology found on Earth.

Sarah Grey died during the experiments, but Jean Grey, unaware of her sister's death, attempts to rescue her from the DODC.

However, she is captured instead and subjected to the same experiments as her sister.

<Mutant Levels> [Omega Level] Mutants with disaster-class abilities. This classification is based not only on current power but also on potential; they are extremely rare even among mutants. [Alpha Level] Mutants with highly versatile and powerful abilities. [Beta Level] Mutants with auxiliary or weak abilities.