I think, technically, Number 24 in Castrum Abania was the first person to live through the Resonance procedure, but it wasn't perfected and left him mentally unstable. He's dead now, as far as we're aware, not a major character, and probably won't show up again but... if he were, technically we'd have 3. I do wonder if his frame/skeleton will show up again like it did in FF6, which he's a reference to, as the Magic Master from the top of The Cultist's Tower. I think that's only described in one of the lore books though.

Also, Garlean magitek is nothing to sniff at. Whether Zenos had Magic or not earlier, it's quite possible that his armor and swords were tuned to do such things. Like, remember when Regula van Hydrus is fought in Azys Lla during the Warring Triad sidequests, he unlocks the inhibitors on his sword and summons that aetherial tiger? Or did I misremember that? I do think Zenos was abnormal before though, prepped for super soldiery since infancy, if not while in the womb itself.

Ok, good to know that it wasn't a translation issue.

It's hard to say what Elidibus is actually up to, of course. They keep a lot intentionally vague, as always. I don't think any speculation of mine has ever been right either haha. I'm just really curious about how these plot points surrounding The Echo and The Resonant will interact, if at all.