To my knowledge back in 1.x Anima was the energy used to teleport. Moving forward it's now what we are using as the core for Anima Weapons. For relics we used the husk of an antiquated original as base material to re-forge a new body. Then began refueling it with spirit energy via soul bonding (all those trials). Later we met Jalzhan and used the Relic as the core for the recreation of a Zodiac weapon. During the last leg for the Zodiac weapon line. We were infusing mahatma as a way to infuse a sense of self in order to recreate how the originals "bonded with the soul of their bearers". The way I read it was to give a sense of sentience to the weapon.
Now with the Anima line. We are taking Anima and making it into something like a soul embedded into the weapon. Like how they say a master swords smith puts a bit of himself into the blades he forged. Only this is more literal. However, ignoring the crystal farming to keep a sense of this being one long side story. By taking all the energy we built into the Zodiac weapon and using it as an energy source much like in his dark materia. Aren't we taking our semi conscious Relic and converting it back into materia. Then reinfusing it with Anima, to make it into the core some kind of living object? It almost sounds like that one relic (Thf Dagger) from XI and how it was said to speak to its owner.
During the second stage there was a comment how it was absorbing Aether as it grew and could eventually pop if it out grew its body. Despite not knowing how summons and elementals work. Does this mean that if it is drawing in Aether in the way they mentioned. Couldn't it eventually become like Odins sword or some kind of primal esc object (Thordians sword) and invoking the memory of its original owner through the current one?
On a side note, am I the only one thinking that kids master is Jalzhan. With his experiment being loosely based on the Zodiac research before we recreated the Zodiac Weapon?