Wanted to get in on the fun with this, but am in a "no new kits until you get through some of that unbuilt queue" mode and didn't have any main protagonists' first suits on the pile.
So bending the theming a bit by asking myself what is the first suit of any ordinary pilot who's not a series protag and so doesn't get to stumble in to some super secret prototype during a surprise attack and immediately and improbably become its sole pilot despite being a moody teenager with no military rank or experience?
That's right, a trainer! (And incidentally one of my fave GWitch MSs—generally speaking I am a big fan of mass production designs over hero suits and the Demi is such a great looking design within that space, R2-D2 head and all.)
Going to take the opportunity of building a relatively simple (and cheap) HG kit to try getting serious with weathering, something I've been wanting to figure out but too afraid I'll screw up and ruin a build. So I suppose it's a trainer in more ways than one!