It stands for Guardian Force. They're ... creatures that you can summon in my world. If you junction with them, they allow you to be able to cast magic, and they basically make you stronger. That's what I had been using, so I know how to cast magic with a GF, but without one...

Maybe it's for the best in some ways. Using GF for extended periods of time can lead to memory loss.

[She was going to have a fun time learning.]