There is yet ANOTHER apocalyptic event that is going to occur that we have to stop.
Creation is going through a phenomena where the absence of both Hydaelyn and Zodiark is causing creation to reset itself via natural causes. Since Hydaelyn was the one who split the worlds and basically maintained that split, her death is now causing the reflections to naturally rejoin themselves to the source, like the source is acting like a magnet to call them back. The source is naturally yearning to be made whole and it's going to force all the remaining reflections to join with itself. When that happens, every single calamity imaginable will befall the source at once, not only killing the trillions of lives on all the remaining reflections, but also killing everyone on the source as well. World then resets itself to before it was split, to basically a prehistoric period before the advent of mankind. Basically like what happened to the dinosaurs. Halmarut calls the impeding apocalypse the Solstice. A complete and utter reset to creation. An inverted big bang where instead of a massive explosion outward, everything gets condensed together.
Halmarut and Calyx are part of a group called the Winterers made up of individuals from other reflections who each have their own plan of what to do with their respective reflection. Halmarut is the presumed leader and her goal is basically the same as it always has been for the ascians, to rejoin the shards. Her reasoning is that rejoining the shards the way the ascians intended will at least save some people, as opposed to not doing anything and just letting everyone die, including the people on the source. So to that end, she's recruited particularly ambitous people from the other shards, shared to them knowledge of summoning, the reflections, their connection and the oncoming apocalypse and told them to do whatever they thought was necessary to make her plan a reality.
So now our current goal is to figure out how to stop this incoming apocalypse without letting trillions of people die. To somehow unite the shards without dooming the people on them. Probably via a connection between all the worlds where it can remain stable, existing in synergy whilst keeping them all separate.
Calyx revealed to us personally that he and Halmarut are going to the Fourth in order to observe one of their Winterer colleagues enact their plan for that shard. He also reveals that while they are all part of the same organization and shared information with each other, not all of them agree with each other and have conflicting beliefs. Calyx tells us all of this because he thinks we have no way to follow him, unaware that hours ago, we just discovered a new way to travel between shards using the key. Before leaving, he spitefully tells us that our altruism to try and save everyone will mean nothing when everyone is dead.