[@Raijinslayer]
Mmm~ I'm guessing the prosthetic arm has some kind of lacrima inside of it?

Nemu comes from a lineage of not-quite-so-human mages that have been marginalized over the years and regarded with suspicion or disgust. Similar to how gypsies in some European countries are treated. [s]As a child[/s] She has a problem with wandering off on her own and playing with the dream creatures she can conjure.
The Cloud Chasers rescued her along with some of their own comrades when they raided one of the Librarium's prisoner transport ships. She been with them ever since.
I guess I could see them acting like siblings, if they had been together for a long time.
Admittedly, I haven't really decided on her age, maybe somewhere between 14-17?
  
Rhett is definitely older, nearly in his mid-30's now. He's a seasoned miscreant and an inveterate liar. Depending on which rumors you listen too, he's a former a spy for a prominent merchants guild, defected officer from the Librarium, assassin from a distant kindgom, or a street hustler who's rampant success landed him in hot water. 
His common phrases are [i]"Truth, like beauty, is in the eye of the beholder."[/i] and [i]"Always remember to shoot a man in the back. It's safer that way."[/i]

Rhett could have easily saved your devil-slaying from a brush with the Librarium, but in all likelihood, it was probably a matter of coincidence that he was there to begin with. He was probably there to steal something and was on his way out when he found your character.