Guarded Stance
Cost: 1 maneuver
Learn: 0 XP (everyone can do this)
Effect: +1d6 (black) to all melee/brawl attacks you receive. +1d6 (black) to all the attacks you make.
Defensive Stance
Cost: 1 maneuver
Learn: 15 XP (+at least 2 other talents)
Effect: +1d6 (black) to all melee/brawl attacks you receive.
Improved Defensive Stance
Cost: 2 maneuvers
Learn: 20 XP (+at least 3 other talents)
Effect: +1d8 (purple) to all melee/brawl attacks you receive.
From Guarded Stance to Defensive Stance you have a net gain: remove the d6 (black) that was added to you.
From Defensive Stance to Improved Defensive stance you have no net gain: you have to pay the die upgrade (from 1d6 -> 1d8) with an additional maneuver.
I think it would be better if Improved Defensive Stance required only 1 maneuver (and completely replaced Defensive Stance, so they couldn't be used together).
And please, add a maneuver similar to:
Evasive Stance
Cost: 1 maneuver
Learn: 0 XP (everyone can do this)
Effect: +1d6 (black) to all ranged/gunnery attacks you receive. +1d6 (black) to all the attacks you make.