|Location||Somewhere within Mugenri|
The Netherworld (冥界 Meikai, lit. "Realm of the Dead") is supposedly the land where ghosts and souls reside after death. The location was first revealed in the second interview, probably based on the Netherworld from the Touhou Project.
The Netherworld is a part of Mugenri rather than separated from it. Save for a few exceptions, one's soul will get led to the Netherworld to be judged for 49 days, where after receiving its due punishment, shall proceed to its next life via reincarnation.
The Netherworld was referenced in the pre-dated game Emergency Everyday: When Shinkuu turned into a vengeful spirit, he astral-projected himself and latch on to Big Boss. This saved him from going to the Netherworld.