The Post-Solar Era began at some point in the future, when sunlight mutated. Its seven colors each granted people different abilities. Red light, for example, let people produce flames, while green made them stronger. Meanwhile, a dark force quietly devoured the land. Animals and plants in the areas it consumed mutated, and those regions came to be known as the Dark Forest.
Over time, four great tribes emerged in the Post-Solar Era: the Divine, Undying, Demonic, and Spirit Tribes. According to scientists, the world not yet corrupted by the dark force is circular. The force is devouring the land from a certain point at its center, so all the tribes are migrating toward the heart of the world from different directions.
The Divine Tribe is the strongest of the four. After negotiating with the other three, it ultimately claimed the central region of the world for itself. There, it built Yuliangmu, the world's premier solar-energy university, where outstanding students from across the world gather to begin a new chapter in their lives.
In the Post-Solar Era, there is a mineral that can store solar energy, called a Sunstone. The Trace Keys are Sunstones containing immense energy. There are seven in total: red, orange, yellow, green, cyan, blue, and violet. Legend has it that whoever possesses all the Trace Keys can cross the Dark Forest and trace the world back to its origin. That is the meaning behind their name: keys to tracing the world back to its source.
The protagonist, Qingmen, begins university life at Yuliangmu. He forms a club called Chasing the Waves, meaning to follow the tide of the times. He and his friends live and study at Yuliangmu, learning about solar energy while investigating the truth behind the Green Trace Key incident, catching the culprit, and protecting one another.
