The Middle Galaxies, also known as the Legendary/Middle Plains, were unimaginably vast, so vast that the Lesser Galaxies or Lesser Plains couldn't compare to them.
The first difference between the Lesser and Middle Plains was their arrangement. Unlike the Lesser Plains, where each layer was divided by the Star Ocean and the Star Ocean Boundary of the Unique Plains, the Middle Plains of each Middle Galaxy were a continent of an unimaginable size.
It is so large that a quasi-legend rank can't reach the end of it, even in its entire life, even if it flies in the air at full speed its whole life, not to mention the dangers hidden in these vast plains. Only a Legendary Rank was qualified to move around here!