Trivia
Zerrinnen is German and means to melt away or to disappear.
Ain's physical body is disappearing, showing his true form.
In most of the maps, the blank background covers every element of decor but in Free Training, the shade of the table and the chairs will be visible.
Herrscher
Even his physical body was a meaningless existence created by the Goddess. By shredding off the shell of his physical body, he becomes a true, complete master of the void.
The master of the void decided to use the shell that he had discarded.
It was a remanant of chaos, that could no longer be called an existence of this world.