How exactly do Calamities and Rejoinings relate to each other?

[ShinShimon]

7/13 is already more than half way. Much of the damage from the seventh was averted, but it was still a calamity and probably triggered a rejoining.

Do we have any evidence of that though? If it only really affects one continent, and leaves every nation there intact, does it really count? It's really only a Calamity to Eorzeans, and a pretty wimpy one at that.

On another note, do we know why Floods are bad for the Ascians? Does rejoining a Flooded shard pose the threat of permanently screwing up the Source? If anything, it seems like it'd be easier to rejoin the 13th than any other shard, because the barrier between it and the Source is pierced regularly without any Calamity.

I wonder if Solus isn't interested in the First and light-aspected Black Rose because he wants the First to be as flooded with light as the 13th is with dark, so that the First can be rejoined at the same time as the 13th and counteract the imbalance.

[Rocl]

If the Ascians consider it a Calamity, it's probably enough. They have canonized the Seventh Umbral Era and its preceding Calamity as a victory and an Ardor, so it seems have been a Rejoining, yes. Elidibus muses if Minfilia surviving the Ardor was by Hydaelyn's direct intervention as early as 2.1--we can safely assume he's referring to the most recent Calamity before anything else here. (And in the very next quest Elidibus mentions "they survived the Seventh Ardor;" so yeah, that Calamity, no matter how wimpy or mitigated, Rejoined a Shard.)

The Floods seem to be bad because when a Shard experiences a Flood, it can no longer be Rejoined. This leaves a lot of questions, like, "how many Shards is enough to revive Zodiark?" because the answer can't be "All of them" if one is permanently incapable of being Rejoined.

Void of its aether, the Thirteenth could no longer be rejoined with Hydaleyn, ultimately losing its value to the Ascians.

Now that my cursory research is done, let's try to put this more succinctly:
A Void of any flavour is bad. The shattering of reality and expulsion of Zodiark carved up the Aetherial Sea into 14 pools. To undo this, the pools, and all of their aether, must be added back to the Source. A void is devoid of aether, so it's worthless. How a Flood of Darkness and a Flood of Light differ in their creation of a void seems ultimately meaningless, because there's no aether left. Whether Rejoining a Flooded Shard with the Source would screw it up... probably? But it's just not worth doing--there's no benefit for the Ascians to do this.

The Seventh Umbral Calamity signaled a Rejoining. No matter how localized it was due to Louisoix's intervention (and let's not forget it did disrupt the Source's aether enough to render linkpearl communication useless for a few days, iirc) it still ultimately resulted in a Shard's aether being folded back into the Source. Both our allies and enemies agree on this matter--the Ascians refer to seven Ardors even when we're not around, and the Encyclopedia Eorzea refers to the Scions and Students both having come to the same conclusion. Each Calamity ushers in a sort of Dark Age, and we're left with few records of what happened earlier. While the Seventh Umbral Era was short, and it was localized, it's important to note we don't know how ANY Calamity affected the rest of the Hydaelyn... outside of, like, the Fourth Umbral? Everything pre-Allag is pretty much unknown, we have legends and lores about Calamities of Wind, Lightning and Fire and descriptions of such... but we know nothing of those Eras, their peoples, their stories. It's impossible for us to know how far-reaching those Calamities were. The Fourth Umbral might've had global implications simply because it ended the Allagan Empire which had conquered the Three Great Continents & Meracydia (and probably much more); we don't know how far the earthquakes actually went--the power vacuum alone would be destabilizing enough. The Fifth and Sixth are the same--we know the seas probably turned to ice in some places for the Fifth, and we know Eorzea was flooded in the Sixth but... those could still be localized events! Especially the Sixth Umbral Era.

I think it's telling that throughout our time in Othard, we very rarely, if ever, hear about any of the Calamities in their histories.

[MrThinker]

Again pointing to the NA fanfest, they said we are trying to prevent an 8th and Final Umbral Calamity. So 8/13 seems good as far as we know.

[waifugenerator]

Wait if a rejoining causes Hyd to absorb a shard wouldn't she be destroying all life on that shard? And is each shard a reflection of the universe or a separate planet altogether cos the game has been very unclear about that. Not understanding how multiple realities can be localized to one planet.

[MrThinker]

And is each shard a reflection of the universe or a separate planet altogether cos the game has been very unclear about that. Not understanding how multiple realities can be localized to one planet.

The dev team actually hasn't decided yet.

[ShinShimon]

A void is devoid of aether, so it's worthless. How a Flood of Darkness and a Flood of Light differ in their creation of a void seems ultimately meaningless, because there's no aether left.

I have a problem with the "void of light" concept simply because you can't have multi-aspected variants of a void; there aren't different flavors of nothing. My pet theory is that the flood of light is also a flood of aether, and so instead of Hydaelyn being drained by aether rushing in to fill the void on the First, it could instead be the sheer force of light on the First actively drawing aether away from Hydaelyn. If Ascians ever use the word void to describe the First (do they ever do this explicitly?) then it's as a result of the practical similarities to the situation on the 13th - the world would become useless to them because of the aetheric imbalance.

But what if the imbalance renders a world useless not because a rejoining is physically impossible, but because a rejoining would cause a devastating imbalance on the Source that would make it practically impossible to cause future Ardors? The weak membrane between the 13th and the Source seems to indicate that, if anything, a full breakdown of the barrier would actually be easier with a flooded world, even if its not desirable.

And what if the more radical school of Ascians, represented now by Solus, are getting impatient with the pace of rejoinings... and likely also a bit paranoid about the odds of long-term success, given the recent and unprecedented number of Ascian extinctions? And what if in response, they (or at least Solus) hatch the idea of finishing off the Flood of Light on the First, so that they can do a quick rejoining of both the Light and Dark-flooded shards at the same time? It would probably be easier than normal rejoinings because of the stressed membranes between these shards and the Source, and it wouldn't cause undue harm to the Source because the aetheric imbalances would cancel out.

...in theory. Since there's never been a double rejoining, or any rejoining involving a Flooded shard, more cautious Ascians like Elidibus might be opposed to this idea - explaining why Elidibus was on board with Hydaelyn trying to save the First. From his point of view, any scenario involving the rejoining of a Flooded world is an unacceptable risk, and so a Flooded First is as useless to him as the void on the 13th. He's patient (or as Solus views it, a bore), so he's alright with waiting to do another normal rejoining with one of the normal remaining shards, no matter how long it takes.

That Elidibus is unaware of Solus's current plans or whereabouts is telling... just what is an Ascian going to do on the First with Light-aspected poison gas? If this is such a great plan, why didn't Solus tell Elidibus anything about it?

[Anonymoose]

Wait if a rejoining causes Hyd to absorb a shard wouldn't she be destroying all life on that shard?

As far as we know, She has zero capacity to control it from the Aetherial Sea; they're blowing out two sides of a dimensional membrane in the corporeal realm.

[Remedi]

8.0 The merged world. Please wait for it /Kappa

[waifugenerator]

As far as we know, She has zero capacity to control it from the Aetherial Sea; they're blowing out of two sides of a dimensional membrane in the corporeal realm.

Inch resting inch resting...I should rly invest in the lore books so I can get more familiarized with the general lore I'm soooo lost

[LineageRazor]

Wait if a rejoining causes Hyd to absorb a shard wouldn't she be destroying all life on that shard?

Yep. This is why she empowers Warriors of Light - to PREVENT the murder of countless millions of people when their Shards are reabsorbed. It's not something that Hydaelyn wants to happen - but as Anonymoose pointed out, she has no choice in the matter once it happens.

In spite of the efforts of Warriors of Light across history, the Ascians have managed to cause seven Calamities so far, and caused seven Shards to be Rejoined. And yes, the global populations of those worlds were all killed as a result. To lay further crimes at the Ascians' feet, it was through their manipulations that the Thirteenth Shard was flooded with Darkness, and the survivors (if you can really call them that) all became Voidsent. The same thing is happening on the First, except with Light, and again said to be due to Ascian interference - and even if we manage to stop the Flood, it's implied that most of the world was consumed by Light before we were able to step in, so there likely aren't many survivors.

So, just in case you were holding on to sympathies for the Ascians, you might want to reconsider. They are not a nice bunch. XD