Vae makes all of Caelle's prosthetic arms herself. Sometimes they need a little tuning up, and it's easier to have her keep wearing it while Vae works on it, so she doesn't have to keep taking it off and putting it back on every time Vae needs to test something. Caelle treats it a little bit like she's getting a haircut -- she gets to sit around and yap for a bit while someone works on her.