The Lore of Splatoon

Warning: This section discusses the ENTIRETY of the Splatoon lore/storyline in great detail and contains pictures. Turn back if you'd rather experience it for yourself.

About 12,000 years ago

Science warns humanity of dangerously rising sea levels, causing the population to break out in war yet no protections were put in place. Meanwhile, an unnamed scientist has figured out how to create a cryogenic capsule that could freeze living creatures for thousands of years. He uses this capsule to preserve his beloved pet cat, Judd, who was also injected with an immortality drug. The capsule also contained a single cell of Judd's DNA, in order to grow a clone of him incase he had awoken in the capsule and felt lonely.
This same professor had also created an AI known as Tartar which was able to record humanity's history, knowledge, and mistakes, in order to pass it down to the next form of intelligent life.

Not long after, the tides had risen so high that the earth had completely flooded, resulting in the extinction of nearly all mammals, and the entirety of humanity.

However, a very small group of humans did survive.
One group of humans had resided in an underground shelter specifically designed for such disaster. This shelter was known as Alterna.
Another group of humans left earth in search of another habitable planet. They created the space shuttle known as Ark Polaris, and brought along many of earth's species in cryogenic stasis, such as bears and other mammals, hoping that they could one day rebuild what was taken from them.
However, this did not work. The shuttle was damaged beyond repair, forcing the crew to go back to Earth, but they never made it. The shuttle orbited around earth for 10,000 years, before eventually crashing back down.

25 years after Earth's flooding, Alterna scientists had began to rebuild an ecosystem within the shelter, creating many inventions such as liquid crystals made from squid. These crystals had the ability to read the minds of other living creatures, changing color in response. The scientists believed they had found the solution to what they were looking for, and began mass producing these crystals.
These crystals had reflected the desires and wishes of the humans. Some of the crystals were used to build a massive "screen" lining the walls of the shelter, creating the false illusion of the Earth's sky.

Eventually, the group of scientists died, and their children grew up never had seen the Earth's surface. Motivated by the desire to see the true sky, they invented the Spirit Lifter, a rocket specifically designed to lift the crew back to the surface. But something went wrong, and the launch failed.
Their shelter had been destroyed by the power of the rocket, causing pieces of what they built to rain down on them. Killing the rest of the humans.

For 10,000 years, the Earth lay stagnant. The tide had came down over the years, yet no intelligent life had ever repopulated land. That was until the liquid crystals of Alterna had began to seep into the ocean, slowly being absorbed by the sea creatures living in Alterna's waters.
These crystals - still containing the human's desires - had passed their feelings onto the sea creatures that had absorbed them, accelerating their evolution until one day they had sprouted legs and began to walk on dry land.

Under construction :,)