[Kelly Pedersen]

Your retreat distance is defined as "1/10th of your Move - exactly as for a step." So, any way of increasing your Move can potentially increase your retreat distance, as long as you can hit that magic number of Move 20. Not easy, of course! However, I'd be inclined to rule that anything that increases step can be used to increase retreat distance, if they're applicable. For example, Martial Arts adds the "Giant Step" option for Extra Effort, which basically allows you to spend 1 FP and make an extra step in the round. I'd allow you to do that for retreat as well, with the restriction that you couldn't do both in the same turn - you could either take an extra step, or retreat 2 yards, not both.

Similarly, there's another optional rule in Martial Arts, "chanbara attacks", that lets a combatant to "trade" attacks from something like Extra Attack or All-Out Attack (Double) for steps. When using that rule, I'd allow a character who didn't take all the attacks they were entitled to during their turn to "bank" those for extra retreat distance. So a character with Extra Attack 2, for instance, if they took only a single attack and thus had 2 attacks left, could use that to take two extra steps on their turn, take one step and then retreat an extra yard while defending, or take no steps, but retreat an extra 2 yards.

For any options that add a discrete number of steps, which can be taken apart from other steps (as both of the above options do), rather than simply extending the step distance (which is what buying your Move up to 20 or higher does), I'd also allow multiple retreats to the character, allowing them to get the retreat bonus against several different opponents, rather than just once.