The Palace is a location in Persona 5.
The Palace is the cognition of an individual with desire strong enough to twist the location in reality where its host expresses his or her innermost desire. Each Palace is inhabited by the Shadow Self of its host, lesser Shadows which fend off intruders and cognitive existences projected by the host. While cognitive existences do not affect their counterparts in reality, because the Shadows still represent the unconsciousness in reality, the Phantom Thieves of Hearts establish the code names for all of their members to avoid identity exposure during their infiltration.
To activate access to the Palace, it requires to input the Metaverse Navigator app with four pieces of crucial information by voice: full name of the host, location of the Palace in reality, title of the host and the form the Palace takes. The Palace serves as the main battleground for the Phantom Thieves, as the main dungeons each represent one of the Seven Deadly Sins. Mementos on the other hand is a Palace that represents the entirety of humans. Each Palace also holds a Treasure, the main center of the Palace host's warped innermost desire. Once that Treasure has been obtained, the host of the Palace will feel deep regret for their actions, and confess to their sins, subsequently that Palace will collapse.
However, if the host's desires are destroyed by the intruder, that person's mental state will deteriorate in the real world and almost enter the vegetative state. If the host is straight out killed, the one in reality will die as well. This is key to the plan of Goro Akechi, who uses the Palaces and Mementos as a way to safely assassinate his targets. The Phantom Thieves prevent mental deterioration by not killing the host but persuading the Shadow Selves to return to their true selves and confess their crimes. In cases like Yuuki Mishima's Shadow, a sound persuasion alone is enough to reform the host's mind without fighting or taking away the Treasure.
Futaba Palace is special that Shadow Futaba does not have full control of her own Palace but loses to the cognition of her deceased mother because the real Futaba has fallen to suicidal impulse due to her regret for her mother's death.
- The Palace is somewhat similar to the TV World of Persona 4, as each dungeon typically reflects the mentality of the one who created. Examples would include Kamoshida, who views himself as the 'king of the school,' and is reflected by his Palace, which appears to be an old castle, and Yukiko Amagi, who's dungeon was a castle that represented her feelings of being locked away by her own birth.