The Earth-like planet that was one-fourth the size of our own collided with Earth, resulting in a catastrophic global event that led to a reduction of over 50% of the human population. On top of this, the arrival of this interstellar object also introduced a powerful species known as the "demon race" who took control of humans. As a result, human civilization was at risk of becoming extinct and could only be found in the final five forest settlements left as the demon race became the new rulers of Earth.
