The Onion Knight began as the freelancer job for the four youths in the original Japanese release. The youths themselves weren’t very spectacular; they were personality-less, distinguished only due to their color swapped outfits. In the DS Remake, the youths have their own personalities and character designs. Final Fantasy III still has the Onion Knight job, but it’s a job one would have to unlock quite a ways into the game.
Yet, as a character, the Onion Knight isn’t in the DS Remake. While it’s typical of a remake to change the core game, it doesn’t quite explain how the Onion Knight arrived in World B. The Warrior of Light, for example, was originally a manikin. He originated in World B, and simply traveled to World A. This isn’t true for the Onion Knight.
So then, where did the Onion Knight come from? Abd most importantly, who is he?
Since the only constant from Final Fantasy III is the world, we can presume that the Onion Knight is one of the four youths from the remake. I believe it would have to be one of the youth, as only they can be warriors of light.
Based on their physical characteristics, it would seem that only Ingus or Refia was the Legendary Onion Knight. Ignus’ hairstyle is similar to the Onion Knight, while Refia’s hair color matches the latter. However, Refia is a girl, and Ignus just doesn’t seem to embody the Onion Knight trapped in World B. Of course, Ingus’ Onion Knight’s outfit is similar to the Onion Knight’s…in the sense that they’re both wearing red.
So then, not the strongest connection.
The Onion Knight’s hair changes to silver, matching Luneth’s, if given another costume. So then, this settles it right? Luneth is the Onion Knight. It would make sense: Luneth and the Onion Knight are flagship representatives of Final Fantasy III. But simply being representatives isn’t enough to explain the differences.
When considering their personalities, we see a marked difference. Luneth is brave and willing to fight any challenge; the Onion Knight is a bit more calculated, preferring to fight only when he knows he’ll win. And none of the other youths seem to have the Onion Knight’s personality either. Arc is timid, only fighting to prove himself. Refia is nurturing if anything. Ignus, while a knight, is more refined as well as well as less impulsive.
Of course, there are two other scenarios. First, maybe none of them are the Onion Knight. Dissidia is simply a homage to the classics, whereas the Onion Knight is more classic than Luneth or Refia. Speaking of which: Luneth, Ingus, Arc, and Refia create the acronym LIAR, as in this child shouldn’t exist.
But I’m being facetious.
A more likely scenario is that the developers combined facets of all children into the Onion Knight.