In Mechanical Heart City, a city where everything is driven by precision clockwork and complex locks, everyone's fate is closely related to solving puzzles. The young "unlocker" Zero has the rare talent of breaking through all mechanical "logic lines", but he can only solve the gaps in his own memory. He wanders among the increasingly spreading "rust" in the city - a mysterious disaster that causes machinery to become disordered and logic to collapse. He numbly repairs other people's lives and searches for his own past.
By chance, he was entrusted with opening a legendary "Lock of Silence", and thus got acquainted with Yin, a tuner girl who could "listen" to the soul of the machine. The two discovered that "rust" was not a simple malfunction, but a conscious erosion. In order to explore the truth, they work together to go deep into the forgotten bottom of the city and fight against the forces of craftsmen who stick to the old rules. When they finally arrived at the "Mechanical Heart Tower", the center of the city, Zero was horrified to discover that the lock core of the city's ultimate lock was actually his lost memory. The key to saving the city is to find yourself, or to forget it forever to protect everyone? This is a cyberpunk fable about memory, order and the human heart.
