In the distant future, the only sentient beings in the world are robots. They are the last remnant of the human spirit. However, mankind is not dead. A technology exists that is capable of transferring memories to these robots. But with limited space, new memories will gradually overwrite the old. To prevent the emotions in human memories from fading away, the robots resorted to converting the emotions to music and storing them in a place called Cytus. The robots use these songs to experience human emotion and dream that souls exist in each of them... Cytus