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The Netherworld (地下, Nezā) is an evil and forbidden area of the Tokyo Empire. Entrance requires permission from The Holy Sol Temple. In reality, it is the remains of the underground train network underneath the nation that was mainly destroyed during the Great Disaster.
As it's forbidden to enter normally, exploring the Netherworld requires approval from The Holy Sol Temple. In the Church's teachings, the underground landscape is an unclean land which is hell for not receiving the light of the Sun God. Due to its sheer size it is home to the White Clad and contains many secrets. Though it has fallen into disrepair, the area around Yotsuya Station has functioning machines and electricity that The Knights of Ashen Flame use for trapping those who come to investigate their territory. Despite theoretically just being train tunnels, the Ash Knights have either found or built temples and churches to use as bases. Despite the official beliefs of the Tokyo Empire, the government and church have various uses for the Netherworld. The Shadows of the Holy Sun are raised underground and are trained for life in the darkness to secretly protect the nation's interest. It is believed that if every pillar was to be gathered her then the evangelist would be unable to reach them, due to her inability to enter the netherworld.