One of the things added to this page was Astaroth. They didn’t appear until much later in the original story. However, I felt it was good to establish a relationship between Eliza and the demon early on (even if it’s only a glimpse). Astaroth won’t be staying for long. There are some loose ends to see to before they join Lord Paix on his way to the capital.
Demons stay close to those with which they share a pact, as a master acts as a magical tether to this world. The bond can be stretched quite thin if the master has a strong aptitude for magic. For example, as Lord Grimsby is quite learned and adept, he can travel to the capital without Stolas. In other demons can travel some distances, but it impacts the form they take and their own ability to perform magic. Demons return upon death since it severs their connection to the human realm.