In the year 2049, Earth lies in ruins, ravaged by an unknown influenza virus that has led to a global catastrophe. Mutated creatures, including zombies and monstrous beasts, roam the decimated world. Yet, on the 4th of May, 2245, a strange phenomenon occurs: time itself reverses, and history rewinds to the year 2044. Chen Yu, a survivor of the apocalyptic future, finds himself thrust back in time before the calamity struck.

Guided by the memories of the future, Chen Yu awakens in a world that doesn't yet know the horrors it will face. In a desperate attempt to save his parents from their tragic fate, he battles against time and the impending apocalypse. Armed with knowledge of the mutations and creatures that will plague the world, Chen Yu prepares to face the challenges ahead.

He uses unconventional methods, such as harnessing the power of low temperatures to slow down the progression of the virus and creating makeshift weapons for protection. As the apocalypse unfolds once more, Chen Yu must navigate a world that grows increasingly chaotic, filled with the sounds of screams, explosions, and desperation.

With the crystal nuclei extracted from defeated zombies, Chen Yu seeks to develop a serum that can potentially resist the virus and its mutations. He is driven not only by the desire to save his parents but also to prevent the dire future he knows will occur if the virus isn't stopped.

Having lived through the nightmare once, can Chen Yu, armed with experience, make a difference this time around, or will it turn out to be a wasted opportunity?

C473 What Kind of Grudge?