To use a physical parallel: think of astral as the muscles of the body. Prana, or magic, is the kinetic energy produced by those muscles. With that energy, we can walk and run and lift a cup of tea to our lips. And while it is certainly possible for the ability to move to be exhausted, it is rarely something so severe that a day's rest will not refresh it.
The contract Archer proposes is not one that would allow him to feed on Tempest's flesh. It is one that would equate far more to carrying him around on her back.
Re: [Late evening]
To use a physical parallel: think of astral as the muscles of the body. Prana, or magic, is the kinetic energy produced by those muscles. With that energy, we can walk and run and lift a cup of tea to our lips. And while it is certainly possible for the ability to move to be exhausted, it is rarely something so severe that a day's rest will not refresh it.
The contract Archer proposes is not one that would allow him to feed on Tempest's flesh. It is one that would equate far more to carrying him around on her back.