A good character concept isn’t maybe the most important aspect of a hero but a suprising and a good idea can give the player more motivation to play with his/her character. Without magic and different races some players can see their options narrowed in world of mice. But as i can see it in Mouse Guard you just have to be more clever.
As 2nd edition is coming and I think many of us are starting this awesome game again, we could share some awesome character consepts we have encountered. I have seen some discussion about “priest” class in MG for instance.
One of my players made a “bird whisperer” mouse. Using his skills in understanding the language and behaviour of birds he was able to give his team many advantages. He also had this flute which was able to make bird voices.