In the megacity of Itherium, happiness is a commodity that can be quantified and traded. The rulers built a false paradise for the elite by extracting human emotions to create "psychic crystals", at the expense of the people at the bottom becoming emotionless walking zombies - "Greys".
Lin Kai, a highly skilled but emotionally numb emotional refiner, just wants to survive in this gray world. Until one day, a crystal containing the memories and emotions of a stranger allowed him to glimpse the terrifying truth about the soul and human nature behind this perfect order.
In order to pursue this trace of echo that should not exist, he met a group of rebels called the "Echoers" who tried to awaken the world, and was forced to embark on a desperate road to betray his own class and fight against the entire world. His mentor, the guardian of the city, is setting up a dragnet to lead him back to the "right path".
When the truth about the world is revealed layer by layer, and when close relatives are involved in the core of the final conspiracy, Lin Kai must make a choice. Destroy this cannibal world, or become its new god?
This is a story about finding hope in despair and regaining heartbeat in numbness. When all emotions are stripped away, can the memory of a kiss become the fire that ignites the entire world?
