9 parts Ongoing I've had this idea for awhile, but I've finally decided to do it.
Error has a job, it is to destroy aus. Whenever he isn't 'working', he goes back to his 'home', the Anti-void. The Anti-void is completely white, however, throughout the centuries, Error has decorated the ceiling with his strings, as well as the SOULs of the Frisks, Charas, and other variations of the people controlled by the Player. The voices often mock him, especially when he needs to do his job. However, there ARE times when they are very quiet, it's when he's met his status quo for destroying aus. Basically, when the balance isn't tipped too far to creation. When this happens, he is able to hear the voices of the SOULs he's gathered. One day, one purposes an interesting idea, and since then the SOULs have taken over the bodies of the puppets Error knits in his spare time. With this, they end up helping Error with his wounds when he comes back from his work, and often likes to watch through the screens Error shows them.
More info in book, but remember, I do not have an update schedule.