Shimabara Hell

Shimabara Hell, is a Reality Marble which is the remnants of Amakusa's original world etched in his soul. Because the reality marble does not allow for the existence of living beings within it, even the air itself is poisonous to those within this world.

It is impossible to escape this reality marble normally, and because the Onri Edo Castle exists in the real world outside of the reality marble, it should technically have been immune to any attacks from within it