The story takes place in a prosperous modern city called "Jiang City". Under the surface of the city, there is an unknown ancient underground ecosystem - the "City of Earth Lines". It is not a ruin, but a sophisticated life support system that relies on ancient acoustic resonance technology and special geothermal energy to maintain operation. Its core function is to regulate the geological stability and ecological environment balance of the entire Jiangcheng area, just like the "heartbeat" of the city.
