The world is called Book, on account of that being Prospective's idea of a "joke?" (whatever that means). The actual planet that her protagonist, Lana, currently lives on (as far as I know) is called Earth.
In this world, there exists a system known as Character Likenesses (usually only Prospective refers to it as such), also known as Entity Classes (Characters refer to it this way, and Prospective may also, from time to time). This classification system can also sometimes be called Perspective Class (not to be confused with Prospective), as that is, at its core, what it technically is—a type of perspective. Maybe this was an unnecessary detail.
There are five known Entity Classes: Prospective, Prospectre, Prospectral, Character, and Creature.
"Prospectives" are the highest level sentient nonphysical entities. They have the power to influence and control physical and nonphysical entities. They typically possess many different Skills.
"Prospectres" are sentient entities that commonly do not have their own physical form, but can also exist with one. Their main goals are to find and keep physical forms, even if that means causing harm. There are both hostile and passive variants of Prospectres. They also possess Skills, and some can have multiple.
"Prospectrals" are non-sentient entities that commonly have their own physical form, but can also exist without one. They rarely have goals of their own and can be both hostile or passive, though the latter is more prominent. It is very rare to encounter a Prospectral with a Skill.
"Characters" are sentient physical beings that typically have the Worker Skill, though there are many who have no Skills. In very abnormal circumstances, a Character can possess two Skills. Humans are Characters, and some animals are also. There are friendly Characters, and there are hostile ones. Any Character that has the necessary Skill(s) can inhabit the forms and bodies of other Entity Classes.
"Creatures" are non-sentient physical beings. They do not have Skills. Some are docile, some are hostile. Their bodies can be used by all of the other Entity Classes that have the necessary Skill(s). Most animals fall under this category.
(Prospective is not a Prospective. The best thing to define her as is the Author.)
The next chapter on world-building will focus on Skills.
(Because I have finished editing chapter 2, I am going to publish that alongside the original insights that have now been removed and provided as references instead.)
(Entities can only inhabit living things, not inanimate objects, such as androids.)