You say that this wear/damage is only 12 inches, not all the way around - do you mean that it is truly only worn for a 12" section of tire? Or do you mean that it is worn all the way around, but you can only see cords in a 12" section?
I still don't think it's alignment, though I could be wrong. >> Need more pics. <<
If it is alignment, that is some of the most extreme toe out wear I've seen. And difficult to believe that one tire has that wear and the other side doesn't (the thrust angle of the front axle is always going to be straight with the direction of travel, so toe wear on the front tires will be about equal)
How many 32nd's do you have left on the rest of the tire? It looks like at least 5 or 6/32nd's in your pic.
Usually toe wear looks more like this:
Note how in this pic, the wear extends inwards into the tread, from the sidewall, an inch or so. I don't see that in OP's pic - I see damage immediately at the intersection of the tread to sidewall, and nowhere else.
Front toe wear will be equal left and right (on the front, at least - you could have toe wear biased to one side on the rear). If you don't see wear on the left front tire, this wear on your right front tire can't be toe wear. Maybe this damage happened when the tires were on the rear of the vehicle and you didn't notice when you did your tire rotation. You would need to be running extreme camber to get wear like this. Camber typically creates more gradual wear across the entire tread like this:
How much are you lowered? (if any?) Do you have camber correction arms in the rear? Like I mentioned, if this happened in the rear of the vehicle, a combination of toe and camber wear may be able to do this to just one tire. Have you taken a close look at the other tires? If you are lowered, have you taken a close look inside the wheel well for evidence of rubbing? (though the mazda5 has pretty good clearances actually) All bushings and ball joints in good condition?