Chen Huang accidentally got a "regret recycling machine" - an old and weird device that can transform his "regret" emotions into physical objects. At first they were just bits and pieces, but as he accumulated more and more regrets, the things spit out by the machine became larger and larger, more bizarre, and even began to have certain obsessions or dangerous attributes of the "original owner". His rental house was quickly filled with everything from lost toys from his childhood, to unsent love letters, to relics that were supposed to belong to "deceased" relatives and friends. Until one day, after the machine vibrated violently, it spat out a strange key with blood stains on it. Late that night, someone knocked on the door of his room, which was filled with debris. The person outside the door claimed that he wanted to "retrieve" something that "should not be here."
