Shimabara Hell Picture Scroll (島原地獄絵巻, Shimabara Jigokuemaki?), is a Reality Marble which is the remnants of Amakusa Shirou'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. Muramasa is able to bisect the castle along with the Reality Marble though with Tsumugari Muramasa because the castle shares part of its name with Edo Castle and name Muramasa is synonymous with the Tokugawa's downfall. It wouldn't have worked if Amakusa Shirou hadn't rhymed the name of his castle with the Tokugawa's own.
- ↑ 1.0 1.1 Fate/Grand Order: Epic of Remnant - Shimosa Province: The Stage of Rivers of Blood and Mountains of Corpses, Chapter 15