Well if they go the power route, I would want to have it be along the lines of Ninja type level powers you saw in anima of Japanese manga. Stuff like invisibility, powers of misdirection, super agility, durability, etc. Like I remember Ninja Scroll where you had Emi Shinohara who was immune to poisons and was the Imperial food taster and so her body was toxic to the point that anyone who so much as kissed her would die.
Point being it should be powers that would aid them in actually carrying out whatever role they have in the TG or AG.