There is a high-dimensional space called the Mio Theater. It captures people with "regrets" in reality - either the dead who have not fulfilled their wishes, or the living who are on the verge of death, and pulls them into a replica world built by "human collective obsession". These copies are not fictions, but "regretful events" that actually happened but were covered up by time for various reasons, such as the scenes of unsolved cases, the ruins of ancient civilizations that disappeared, and spacecraft that were not successfully launched, etc.
Real historical figures will appear in the dungeon, but their characters will be distorted by "obsession" and will no longer be what they look like in the history books.
Purpose: to make up for regrets