When Did I Become a World-Ending Anomaly?!

On July 8, 3065, a colossal meteorite crashed into the middle of the Long Ocean on Blue Star. In an instant, it triggered a massive earthquake, followed by a tsunami hundreds of meters high. The waves swallowed countless island nations, and seawater surged hundreds of kilometers inland across several continents near the Long Ocean. Strangely, several days later, when the waters receded and the flooded cities reappeared in the sunlight, the people and many large livestock, cats, dogs, and other creatures were still alive, except for the chickens, ducks, little cockroaches, and similar creatures! But the cities had been ravaged by seawater, leaving their water and food supplies unfit for consumption. Even the land could not be farmed for the time being after being soaked in seawater. All the cars and electrical appliances were ruined after spending several days underwater. To address the shortage of drinking water and food in coastal cities, the government sent large numbers of trucks and trains to deliver supplies. But they discovered that, due to the scarcity of food and water, these so-called living creatures had begun attacking and devouring one another, and were growing stronger and stronger! Thus began a century-long war against the uncanny, and our protagonist was born into that war!