Headcanon for soul crystals

[Anonymoose]

I was wondering <...> if it was a randomly picked up stone in which we imbue our knowledges and techniques <...> or is knowledges that crystallize themselves in a stone (whether it's out of the owner's volition or not)

Soul crystals are purposely manufactured. They are a tool that was invented in the past. When a group of people shares a culture and school of thought around a highly specialized and demanding combat style, they sometimes create soul crystals to support that group. You wear it close to your skin and it passively "records" your memories and skills and experiences, but also you can use it as a focus to channel aether through if needed. This allows some schools of combat to develop extremely intricate, powerful abilities that the human body cannot otherwise handle. (For example, some advanced black magicks can burn the spellcaster alive if a focus is not used.)

It also allows them to pass down that knowledge and experience (which might otherwise take a lifetime to learn) much easier. If you wear a soul crystal that had previous owners, it's not only "recording" your experience, you can access the experience of its past owners, as well. (As long as you can attune to it; you have be able to "vibe" with its past owners.) The current owner of a soul crystal is potenitally capable of becoming the sum of all its past owners - hopefully catching up to them; ideally surpassing them.

FFXIV 1.0 did not have jobs, just classes - just basic schools of training around the use of specific weapons. There needed to be an excuse for why jobs were not within reach until then, and the excuse was that those little cultural groups who developed and trained people in those arts were either small/selective/far away, or have fallen out of use entirely. The whole story angle was that the Empire and the Calamity were such a big threats that we had to acquire these mysterious ancient arts if we hoped to fight back. That's why most of the job stones have previous owners.

But that's not necessary. Stephanivien is mass-producing blank Machinist job stones right now and we're the "first generation" in his tradition of combat.