Splatoon 3: What Is Alterna?

thegamer.com:

In Splatoon 3's Hero Mode campaign, following a brief fake-out in Splatsville's Crater, it is revealed that there is a gigantic domed city located underground. This city is named Alterna, and it's the staging ground for a planet-threatening scheme that can only be stopped by Agent 3 and the Current Squidbeak Splatoon. Putting that whole adventure aside for a moment, though, just what exactly is Alterna?

RELATED: Things We Wish We Knew Before Starting Splatoon 3

It's made clear that nobody living on the surface knows of Alterna's existence, while Alterna itself is borderline abandoned, save for the minions of the malicious force perpetrating the aforementioned planet-threatening scheme. So where did this mysterious domed city come from? Let's take a trip back in time to discern the origin of Alterna, and perhaps learn some major truths about Splatoon's setting in the process.

Please be advised that we'll be getting into some spoilers for Splatoon 3's Hero Mode.

In a time long, long before the age of Inklings, Octarians, and the myriad of marine-turned-terran life forms that fill the world of Splatoon, there was an odd little race of beings known as humanity. These bipedal mammals covered the entire world, building their own civilizations, living their lives, and perhaps most importantly, innovating in the world of science. Sadly, that endless thirst for progress resulted in conflict, which eroded the planet's stability. At the peak of humanity's accomplishment, the Earth itself bore its fangs, striking down civilization with terrifying natural disasters. Volcanoes erupted, seas swallowed cities, and humanity began dying off at an unprecedented rate.

However, all was not lost. By chance, a small coalition of people