"This world is our home. We have lived here since the beginning of life on earth."—Dr. Andrew Golsue, 3926.
The homeworld for humanity.
Post-Überschwemmung
Terrain
The earth is a desolate ocean planet. The entire world is covered in water with only mount everests tip sticking out about 3 meters at low tide. Though even everest is doomed to one day be eroded down below the ocean.
Beneath the ocean depths lie the old continents still largely intact though most regions have been eroded down.
Biology
On the whole of the world every terrestrial lifeform is wiped out, including humans. (not the ones that moved to Aldea or Hawthorne tho) Not only is terrestrial life now dead but so is all life that requires high saline contents. All the added water is fresh water so most saline dependent creatures would die, have to evolve to not need it or require a lower amount of saline.
On the surface there aren't any landmasses though the occasional algae mat may cover a large portion of water. The biggest algae mat on earth so far has been recored to be roughly the size of Belgium. Theoretically they could grow up to the size of Afrika if they hadn't had any predators.
Due to the now increased ocean area (pretty much the whole world) this allows for whales to thrive as they now have much more room to operate in. Numerous new species begin to arise in the new mountainous underwater terrain.
Remaining on earth there is one singular sentient being left. A sentient robot that was abandoned on a military naval ship after killing a mother and her child, having mistaken the both for members of a terrorist group. This robot was named Machwell after being discovered by a teenager attempting to survive the floodening earth.
Countries
Naturally post-überschwemmung no countries (on earth) remain standing.
Main story post-überschwemmung
The main story (on earth) after the überschwemmung revolves around Machwell as he learns to deal with no longer having a function, needing to reprogram himself and needing to make sure his ship stays afloat. Oh, and the loneliness.