Echo Out of Bounds

At night in Rongcheng City, a sound that is not on the program list occasionally comes out. Sometimes it wakes up from a powered-off mobile phone, sometimes it comes out of a powered-off speaker, and sometimes it only rings in someone's ear. Those who hear it will be temporarily absent-minded, as if being called by something, and then enter a dark night that cannot be recounted externally. Li Tang was a musician, and his ears were so sharp that he could hear the beats in the sound of rain and the strangeness in the crowd's silence; Liu Lu was his brother for many years, and he never had a straight line, but he could always pull people back from the edge of collapse even in life-or-death situations. After the two of them were stared at by the same voice, they began to wander through strange things: in some places, the mirror would speak for you first, in some corridors, the footsteps would be returned to another person, and in some nights, someone would answer "Yes" for you even though you didn't speak. They don't know where they will be taken next time, and they are not sure whether the people who come back each time will still be their original selves. The only thing that is certain is that the voice is never late, and behind it, there is always the same vague name - Echo.