During a time of chaos, superheroes appeared, and the world became peaceful once again. Two brothers who admired the so-called "Earth’s saviors" vowed to become heroes together, but in that world, people are categorized into groups of "Heroes" that protect, and "Mobs" who clean up the mess after. The younger brother Hiiro is a "Mob", while the older Ao is a "Hero". However in times of crisis, especially if their childhood friend Iruka is involved, Hiiro will jump into danger without hesitation!