Ultima Weapon?

[Alynn]

Why did Hydelyn have to directly step (more specifically how did Lahabrea tamper with it to make it so) in during Ultima/ why was it so taxing on her? Should we expect the same thing for Omega since that's a weapon as well?

[Anonymoose]

When the Garleans found Ultima buried beneath Ala Mhigo, they couldn't get it running. To power it, Lahabrea gave them an ancient artifact known as the Heart of Sabik (what I believe to be a piece of auracite-like Dark Crystal). While the Heart got the thing running, the energy of the primals captured by Ultima also woke something within it allowing an ancient magic known as Ultima to be utilized.

This Darkness-based attack is extremely powerful - as you can tell by what it did to the Praetorium. There's a good chance you would have been annihilated if the blessing of Light didn't act as a shield.

Despite being within the Aetherial Sea as we know it, Hydaelyn is very weak, and grows ever weaker when She gives pieces of Her power away or acts through the Crystals of Light to influence the corporeal world. The act of shielding us against something as powerful as Ultima put a pretty big dent in her reserves.

[Cilia]

There are a number of hints that the Ultima Weapon, and the Ultima spell, are both direct manifestations of Zodiark's power / will. This is arguably because the Heart of Sabik, implied to be some manner of Dark Crystal, acted as the Ultima Weapon's core.

Thy foe is Darkness clad in steel.

... [T]he hammer of Darkness must needs be brought to bear upon the shield of Light.

Behold but a sliver of my god's power!

As such, directly resisting Zodiark's power on the corporeal plane would be difficult for the already-weak Hydaelyn. Ultima is an extremely powerful spell, implicitly a direct manifestation of Zodiark's power - so it would stand to reason that it would take an equal or greater amount of Hydaelyn's energy to protect us from it. With very little strength left and even less after protecting us from Ultima and helping exorcise Lahabrea from Thancred, She has been unable to communicate with us often since.

With few details on Omega, none can yet say if it is as anathema to Hydaelyn as Ultima (Weapon) was. It does possess more power and destructive potential (wrangling Bahamut and going toe to toe with Shinryu vs. fighting the likes of Ifrit, Titan, and Garuda), but without knowing if it has a core akin to the Heart of Sabik (Darkness) powering it...

[Anonymoose]

There are a number of hints that the Ultima Weapon, and the Ultima spell, are both direct manifestations of Zodiark's power / will.

Thanks; name-dropping Him rather than leaving it at "Darkness" probably would have helped, lol.

without knowing if it has a core akin to the Heart of Sabik (Darkness) powering it...

<struggles to hold a straight face> Perhaps ... Nero ... after leaving the Praetorium, heard the boom of Ultima and rushed back to find out what could possess that much power, thereby taking possession of the Heart of Sabik from the disabled Weapon and enabling the escape of a mortally-wounded Gaius van Baelsar, these two facts utterly hidden since as they await the perfect time to play their trump card: The Battle of Ala Mhigo!

Orrr Elidibus just gave it to Nero or Teledji or whatever.

Either way, the Heart of Sabik was allegedly going to make an appearance before 4.0, but never did. From the deepest chasms of my paranoia, something whispers that perhaps this was because certain facets of the story were shifted around a bit to connect Omega to the main story arc (since feedback from Alexander included it feeling isolated or separated or "not like Coil"). The sudden throwing of the eyes over the bridge, the lack of serious foreshadowing to the events of 3.56, the need for Alphinaud and Kan-E-Senna to explain what the hell just happened via text exposition alone ... it'd explain a lot, lol. Perhaps it made an appearance after all. </darksteelfoilhat>

But even so, utilizing the blessing of Light on the same scale again would probably undo what energy we gave Her back in 3.4 and put her back in serious jeopardy. She at least needs the strength to maintain Minfilia as her emissary for now, right? If Sabik was indeed here, I suspect we'd try to find another way to deal with the spell now that we know that it's a thing. And if - as Chrono lore suggests - the Bend of Time is a pocket dimension, we might use that to our advantage to rid of us both <holds flashlight to face> and thus cement the fanon that FFV's Omega came from FFXIV.

[Singularity]

Is it documented anywhere that the Heart of Sabik was installed by the Garleans? It doesn't seem to make sense to me.

When Lahabrea is talking about it just before he activates it to cast Ultima, he mentions that it's something "whose surface even the vaunted scholars of ancient Allag failed to scratch", meaning the Allagans certainly had access to it, yet apparently they did nothing at all with it?. From a visual standpoint, the Heart seems pretty well-integrated into Ultima's upper torso. It looks, to me at least, like it was designed to be there from the start.
He also states that it is "the weapon's core" and he does so in a way that suggests he is telling Gaius this for the first time. Might just be my own skepticism, but I find it somewhat unlikely both that the Garleans had the technical ability to replace the very core of an Allagan weapon (though I admit it may have been done under Ascian instruction) and that Gaius was not kept informed of this at all considering it was his flagship project.

As an aside, if the Heart was added by the Garleans, then it seems likely that "The Ultima Weapon" is not the thing's original name, as the Allagans would never have heard of Ultima. Barring a remarkable coincidence, it would probably have been named that by Lahabrea when explaining to Gaius what the thing was.

[Anonymoose]

Is it documented anywhere that the Heart of Sabik was installed by the Garleans? It doesn't seem to make sense to me.

I think it's perhaps all of the above and people are getting caught up in the wording; there's more than one way to gift someone a power.

Lahabrea, who had gifted Gaius van Baelsar the Heart of Sabik and brought Eorzea to the brink of destruction once before

However, it later came to light in a report delivered to the Eorzean Alliance by the Scions of the Seventh Dawn that, despite the best efforts of Nero tol Scaeva, the Empire had failed to reactivate the Ultima Weapon on its own. It was only after Ascian intervention that they had managed to awaken the monstrosity—by harnessing the power of the Heart of Sabik, an ancient relic infused with vast quantities of aether.

The Heart of Sabik is aetherial; it's full of aether, has magicks hidden within it, and was stirred by captured primals. Even if the Heart had never left the Weapon itself, the Garleans probably would have had a hard time kick-starting it. Remember the scenes where Alisaie and Alphinaud waved their hands and manipulated the aether and Dalamud's mechanics obeyed and reacted? A Garlean would have just stood there like, "Hm. So ... it's off?"

[Singularity]

Yes I can agree with that. It seems more likely that the Ascians simply taught the Garleans how to activate it (or activated it for them) rather than gave them an entirely new power source for it.