The world has become too cold.

The warming that had been advancing over a long period of time suddenly reversed at one point. What was once symbolized as the threat of climate change through rising temperatures abruptly shifted to a rapid cooling. The cause remains complex and is still not fully understood.

One theory suggests a decrease in solar activity. The disappearance of sunspots, changes in the magnetic field, and a reduction in radiative energy—all of these may have drastically disrupted Earth's energy balance, leading to a drop in temperature. However, this alone does not provide a complete explanation.

Another theory posits that secondary disasters brought on by global warming are to blame. The rise in temperatures caused the rapid melting of polar ice, releasing vast amounts of freshwater into the seas. As a result, the circulation of ocean currents was disrupted, and the flow of warm water in the oceans stagnated. This cascading effect eventually led to a global cooling—something researchers have speculated.

Furthermore, changes in the Earth's atmospheric composition were also observed. A subtle decline in oxygen levels and fluctuations in atmospheric pressure have been recorded, though it remains unclear how these changes are connected to the cooling. However, the extreme cold has altered atmospheric particles, and the sky now gives off a different impression than before. Even on clear days, the once vivid blue of the sky is almost never seen.

What is certain is that Earth is now trapped in ice.

The oceans, once expansively blue, have turned into vast stretches of ice. Humanity has been forced to shrink its living areas, gathering in the few remaining warm regions and seeking ways to adapt to the extreme environment.

Energy resources such as oil and natural gas have not been exhausted, but extracting, transporting, and utilizing them has become more difficult than ever before. In the extreme cold, machines frequently break down, and even when fuel is burned, it no longer generates enough heat. The functions of cities have slowly deteriorated, and people, wrapped in thick winter clothing, have begun to nostalgically recall their past lives.

However, the most serious impact of this cooling has been on young women, whose temperature regulation systems and hormonal balances have become critically unstable. While medical research continues, it is an undeniable fact that many young women are now struggling to maintain their body temperatures. Their temperatures have dropped, and their menstrual functions have ceased to work properly.

"Cold"—it is no longer just a sensation, but a clear and present sign of impending danger to survival.

Menstruation has stopped, pregnancy has become difficult, and more women are losing their physical and mental stability due to hormonal imbalances. This phenomenon is occurring simultaneously in various parts of the world. One doctor referred to it as "the quiet beginning of extinction."

The outside world was simply too cold.

Then, what about the world inside her?