Regarding Witches

The definition of a witch is vague, but according to the generally accepted theory, one becomes a witch at the moment they gain possession of a power surpassing the boundaries of Humans that they can use at will.

The world, or Fragment, in which they can use their power freely is known as their territory.
Most witches cannot leave their territory at will, but those who can travel freely across the world of Fragments are called Voyagers.

In the story, Bernkastel and Lambdadelta belonged to this special category.