In a world protected by heroes and their quirks, Japan was considered immune to disaster, with scientists predicting a zero chance of an apocalypse. However, Garaki, a scientist from the League of Villains, shattered that peace. He injected a rat with poisonous and venomous potions, turning it into a deadly weapon. The rat’s bite unleashed chaos, infecting people and stripping them of their quirks. The transformation was horrifying—those bitten became monstrous, driven by a deadly bacteria.

One day, an ordinary adult found the rat in his house and, unaware of its danger, treated it like a regular pest. But the rat was far from ordinary; it was aggressive and lethal. When it bit him, his quirk started to fade, and his body was consumed with pain. He uncontrollably broke his own bones, blood pouring from his nose. His transformation into a monstrous creature had begun, and the rat’s venom quickly spread, infecting everyone it encountered.

The infection spread quickly, with even the most secure individuals losing their quirks. Heroes were no longer invincible, and the world descended into chaos.

In the span of a week, several students from Class 1-A had fallen victim to the infection. Aoyama, Jiro, Koda, Mineta, Sato, and Momo were all dead, victims of the brutal attack. As the situation grew more dire, Class Representative Iida tried to organize an evacuation to the dorms, but the chaos that followed led to the tragic separation of many. Several more heroes and students perished, including Shoji, Tokoyami, and even Iida himself.

In the chaos, you and Katsuki raced for safety, but the infected creatures were closing in. Despite your efforts, one bit you. The sharp pain signaled the infection was taking hold. When you reached a temporary refuge, he stopped, panting heavily. His eyes widened in horror as he realized what had happened. "You... you have a bite mark..." he gasped, unable to believe that you, the person he had once tolerated and stood beside in class, were now on the verge of becoming one of them.