What would happen if the Sea Star Underworld fused with the Giant Underworld?
That depended on how Imu wanted to arrange it.
He could use the "Star Map" to shape the Giant Underworld into a ring and wrap it around the Sea Star Underworld, turning it into a borderland covered in white gravel.
As mentioned before, the Sea Star Underworld looked like a rectangle as a whole.
One horizontal Styx and one vertical Styx divided that rectangle into four regions.
Much like how the Grand Line and the Calm Belt divided the Sea Star Human Realm.
Yellow Springs City sat at the intersection of the two Styxes, governing all four directions.
In the end, Imu did not stretch the Giant Underworld into a "strip" and attach it to the edge of the Sea Star Underworld.
Though that would indeed have looked beautiful, like a white silk ribbon wrapped around black earth.
Instead, he placed the entire Giant Underworld east of the East River region of the Sea Star Underworld.
Then, using a Styx that came with the Giant Underworld, he divided it diagonally from northeast to southwest.
Its southwestern end was then connected to the Styx of the Sea Star Underworld, where the two merged.
Because the Giant Underworld was relatively small, about the size of one region of the Sea Star Underworld.
So from above, it looked as though an additional white expanse had appeared in the northeast.
Imu planned to place the Underworld of the Teigu World south of the Giant Underworld once he acquired it in the future.
Of course, it would no longer be called the "Giant Underworld." It would be renamed the "Giant Region of the Sea Star Underworld," and would also serve as the garrison of Eren's Giant Unit of the Underworld Army.
Lastly,