Hey! I have a character that I've been wanting to make and this guild fits her intended back story pretty well! (Actually, she's a recycled D&D character lol).
This is her back story: abandoned at a young age, she was found starving and freezing in the streets by a mysterious man. This man took her in and raised her to become an assassin/master thief.
Maybe the person who took her in was a Mountain Cat or if this organization isn't that old (she's around 19-23 years old), she fell into joining because assassination and thievery is all she knows.
I dunno. What do you think, Spice?
Edited cause I have a good idea on a backstory. 8)
Edit (again):
Here she is! She's is a master assassin; one of the best at her job. She's very good at getting in, killing cleanly, and getting out with out anyone noticing. She's also very good at intrigue and gathering info from the shadows. Nev is definitely a lone-wolf kind of character. Hope she fits in well! :)