In a fictional future world where people's hearts grow increasingly indifferent, everyone both yearns for the warmth of human hearts from the past and discards their own warm hearts. In the past, cities were divided into many districts, each inhabited by people who possessed distinct moral traits. However, in this fictional future world, all cities have become more and more alike, and people have turned as cold as steel. It is only with Momo's arrival that people gradually rediscover their true selves, long buried beneath layers of masks.