Factory is a place where hunters of the STN-J send the witches that they have captured. The place is run by Takuma Zaizen who also runs the Japan's branch of Solomon. Factory is used to manufactor Orbo, a special liquid used to stop witches. The hunters don't know what is going inside the factory or how the Orbo is being produced. It is also a secret from Solomon. Which is why there is an agent inside the STN-J to find out more about it for them.