Shimabara Hell

, 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. Powerful magical energy seeps into the fabric of the world with its presence, with Onriedo Castle becoming bastion of demons that threatens to desecrate the world. Once cast, it crushes the will of its victims and twists humans in its range into monsters. It does not transform every human it finds, some remaining unaffected by chance. But in an instant, one person can find herself beset by monstrous neighbors. A man could find that his wife had become an oni. A mother, that her children had become beasts. Those unfortunates with no magical resistance are simply altered, human norms switched with beastly urges, and they begin devouring humans around them. Fate/Grand Order: Epic of Remnant - Shimosa Province: The Stage of Rivers of Blood and Mountains of Corpses - Section 15: Ultima Cantica: The Stage of Carnage, Onriedo (Ending)
It is impossible to escape this Reality Marble normally, and because the Onriedo 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 Onriedo Castle along with the Reality Marble though with Tsumukari 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.
==References==
Category:Noble Phantasms
Category:Reality Marbles
Category:Unknown rank Noble Phantasms
Category:Unclassified Noble Phantasms
Category:Noble Phantasms introduced in Fate/Grand Order
Category:Noble Phantasms of Amakusa Shirou Tokisada