Phenomenon 001, having risen from the Blood Sea after the disappearance of the Ancient Crete Kingdom, replaced the old sun and illuminated the world of the Deep Sea Era.
For ten thousand years, this massive light source operated as if eternal, bringing not only light and warmth but also a stable order to daytime—if not for it, the City-State civilization as we know it would never have existed, and the entire world would likely be engulfed in a terrifying perpetual night, with all life that once thrived under the protection of the Ancient Crete Kingdom perhaps having silently perished in some ancient era.
No one thought that Phenomenon 001 would one day have problems, just like no one considered whether the Endless Sea might dry up one day.
However, it now seems that this "eternal" sun wasn't truly eternal.