How many souls do you think a blessed sibling has?

[Cleretic]

Later on, when he gave himself all the souls, was the effect mostly just making himself very ill or was he just not that strong to begin with?

Zoraal Ja's strength in that moment is irrelevant. He consumed more souls than his body could take, it kinda doesn't matter how big the cap is when you eat all of the souls. We saw the soul supply both before and after that stunt; he ate hundreds at a lowball! I don't know how many souls a body can take before they hit a maximum, but it's well below that!

If anything, the fact he managed to mostly retain his composure for a while and just looked kinda drunk-sick puts him in the upper tiers.

[fulminating]

I don’t think it is that irrelevant - reattaching bits of the same soul seems to have affected density far more than strength for instance. Formerly ryne until the retcon, the wol, graham and potentially krile are all at 9/14th and not notably stronger than other denizens of the source - or more pertinently the first, ninth and thirteenth.

Taking the two souls thing literally, blessed siblings do seem to stand on a higher baseline than one souled people. Similarly zarol ja, mr snakes from vanguard and the arcadion fighters all seem to get notably stronger wearing a foreign soul. This does seem to also have some pretty bad side effects such as killing you and needing souls to use. I think zarol ja is the only individual we see fight without, with an extra and with a lot, so the main source of extrapolation about how much impact it might have.

There is the potentially similar effect from eating all the light wardens, but I don’t remember that impacting strength, just soul composition until the side effects started and ryne had to use the soul glue.
Likewise it seems that the resonant business is more of a matrix style learnt skill than stat increase, despite using a lot of people as fuel. Since zenos should have had natural echo it does raise a question of why he had the crazy eyes as well, but it might be another side effect. I don’t remember if my cup brimmeth over with ice and fire guy had the same eyes, or the hypertuned but I think they’re a bit different.

[Cleretic]

I don’t think it is that irrelevant - reattaching bits of the same soul seems to have affected density far more than strength for instance. Formerly ryne until the retcon, the wol, graham and potentially krile are all at 9/14th and not notably stronger than other denizens of the source - or more pertinently the first, ninth and thirteenth.

Taking the two souls thing literally, blessed siblings do seem to stand on a higher baseline than one souled people. Similarly zarol ja, mr snakes from vanguard and the arcadion fighters all seem to get notably stronger wearing a foreign soul. This does seem to also have some pretty bad side effects such as killing you and needing souls to use. I think zarol ja is the only individual we see fight without, with an extra and with a lot, so the main source of extrapolation about how much impact it might have.

I might be explaining my read of this badly, but I'll put it this way:

My gut feeling is that your average person in FFXIV's universe might have about the internal capacity to handle five souls' worth of extra aether without having major problems. Five is essentially an arbitrary number here, but it definitely seems to be a relatively low number, going by the void arc in 6.x. The blessing of light (or save that, a warding scale) probably helps in some cases, but they were put into action when dealing with raw aether rather than souls, which might be a different situation entirely. 6.x also suggests some people might just have more capacity for this than others, but it's hard to tell what could be doing this, or if it's even actually a greater capacity and not just, like, a personal indifference to the consequences; the voidsent are weird here. Still, we'll allow that some people might just have a bigger capacity, but I doubt it's by orders of magnitude.

All that means that I ballpark that your average FFXIV-universe person has the capacity to fit a single-digit number of souls in them before things get messy. It seems possible you can notch up the amount there somehow either by personal effort or just pure genetic luck, and there might be differences between shards even outside of the fact the Thirteenth is its own weird thing here; Zoraal Ja's from the Source so that last part doesn't really matter, he's at our baseline anyway.

But it doesn't really matter if your personal capacity is five, eight or ten if you decide to go eat eight hundred of them. I think he gorged himself so enormously beyond capacity that any personal barriers no longer mattered; nobody could possibly be strong enough to eat all those souls and remain okay. It's not a personal failure that he couldn't, although it's probably a personal failure that he tried.

[fulminating]

Hraesvelgr and elidibus also have taken on other souls with few side effects, especially if you disregard the whole mad primal thing. Hydaelyn as well, but that’s weirder with eating them for energy. I don’t know, there just seems to be something going on with soul assimilation and/or modification that I’m missing a key part of. I’m not expecting it to turn into the matrix 3 either, but that golden divot prophecy mentioned souls too I think? Maybe it’s just a reference to another game, it’s not like souls is an entirely novel territory for the series.

[Dikatis]

Hraesvelgr and elidibus also have taken on other souls with few side effects, especially if you disregard the whole mad primal thing. Hydaelyn as well, but that’s weirder with eating them for energy. I don’t know, there just seems to be something going on with soul assimilation and/or modification that I’m missing a key part of. I’m not expecting it to turn into the matrix 3 either, but that golden divot prophecy mentioned souls too I think? Maybe it’s just a reference to another game, it’s not like souls is an entirely novel territory for the series.

Hraesvelgr has done it with one soul who he was already in tune with. Elidibus possessed countless bodies over generations and suffered from dementia, memory loss, and a loss of identity and purpose beyond his role as Zodiark's vessel, to the point of neglecting to use the one thing that could keep his mind intact even when requested to by one of his closest friends. Lahabrea went from a stoic man of reason to a cackling madman who revels in sadism and acts of wanton destruction after absorbing Hephaistos, who was infused with Athena's memories and personality. Emet-Selch didn't suffer this level of degeneration because he didn't jump into as many bodies and took repeated rests.

We also know that devouring tons of souls can muddle your sense of identity, which is why Zero refuses to devour the souls of her fellow voidsent despite being more than capable of doing so. Even the sovereigns of the void risk being torn to pieces by the souls trying to escape their body if they are ever defeated, which is why we don't encounter the Cloud of Darkness in our second foray into the void after we pummeled her with the help of 23 other adventurers + Doga and Unei.

[fulminating]

Hraesvelgr has done it with one soul who he was already in tune with. Elidibus possessed countless bodies over generations and suffered from dementia, memory loss, and a loss of identity and purpose beyond his role as Zodiark's vessel, to the point of neglecting to use the one thing that could keep his mind intact even when requested to by one of his closest friends. Lahabrea went from a stoic man of reason to a cackling madman who revels in sadism and acts of wanton destruction after absorbing Hephaistos, who was infused with Athena's memories and personality. Emet-Selch didn't suffer this level of degeneration because he didn't jump into as many bodies and took repeated rests.

We also know that devouring tons of souls can muddle your sense of identity, which is why Zero refuses to devour the souls of her fellow voidsent despite being more than capable of doing so. Even the sovereigns of the void risk being torn to pieces by the souls trying to escape their body if they are ever defeated, which is why we don't encounter the Cloud of Darkness in our second foray into the void after we pummeled her with the help of 23 other adventurers + Doga and Unei.

I am relatively sure CoD had already mostly reformed by the time the WoD exit cutscene was over?
Elidibus also ate the partially summoned heroes from across the rift around the seat of sacrifice trial. As with hraesvelgr, these souls would be very attuned to him (salvation given form, summoning specifically the heroic bit).

Good shout about the body hopping and Athena+laha fusion dance, I completely forgot about that. Maybe ascian prime would fall under the same umbrella?

[Cleretic]

Elidibus also ate the partially summoned heroes from across the rift around the seat of sacrifice trial.

Citation needed.

A particularly good citation is needed, in fact, because we know that one of those 'partially summoned heroes' was in fact definitely not eaten. You've gone very far beyond both your own point and the original point of the thread, but I really want to see where you think you're leading.

[fulminating]

He turned them from guys posing into balls and then casts lb4 during the mandatory tank lb3 or off yourself and grab a res part of sos. Could you also give the duty finder description a read for me? I think it’s faster than watching the cutscene and both it and the journal mention summoning and taking into himself. The converging light quest also says it’s a partial summoning of the hopes, which must live in either the memory part of the soul or the blue bit. This has to be true as the exarch spell doesn’t do bodies and that is explicitly what is used to call them across to be fodder enemies and/or an Easter egg. Hildebrand as an exception since he was gently stored in the interdimensional greg place.

I guess we can blame ultima the not the primal one. Or the great serpent of ronka. Something’s funny with souls, I don’t know what it is but there’s a few full ones just recently dropped into the lifestream. Maybe it’s just some kind of spiritual tax.

[Cleretic]

He turned them from guys posing into balls and then casts lb4 during the mandatory tank lb3 or off yourself and grab a res part of sos. Could you also give the duty finder description a read for me? I think it’s faster than watching the cutscene and both it and the journal mention summoning and taking into himself. The converging light quest also says it’s a partial summoning of the hopes, which must live in either the memory part of the soul or the blue bit. This has to be true as the exarch spell doesn’t do bodies and that is explicitly what is used to call them across to be fodder enemies and/or an Easter egg. Hildebrand as an exception since he was gently stored in the interdimensional greg place.

I guess we can blame ultima the not the primal one. Or the great serpent of ronka. Something’s funny with souls, I don’t know what it is but there’s a few full ones just recently dropped into the lifestream. Maybe it’s just some kind of spiritual tax.

Fair enough, I'm gonna be honest, that part of the story's a bit rusty for me.

I don't think Elidibus is exactly standing up as a positive example of cramming a bunch of souls in you, though. Like Dikatis pointed out, Elidibus' mental state was in complete tatters thanks to his whole 'being Zodiark' thing; if anything Zoraal Ja handled it better than him, he seemed to mostly remember everything.

Hraesvelgr ate one person, and frankly I wouldn't call him mentally okay either, but largely for different reasons.

All this to say: 'eating a bunch of souls' has historically not gone well for anyone at all; in fact, just eating one soul doesn't have a great track record. It really shouldn't be surprising that it went badly for Zoraal Ja too, especially given, as I keep pointing out, the absolutely insane amount of souls he consumed. So, to go back to your original comment: it made him very ill at first, and then it made him a lot worse than that, and none of that is because of his personal strength, that was just a bad idea all around no matter who does it.