

Persona 3 Em is a mobile RPG that serves as a side story set during the Yakushima trip from Persona 3. It mirrors the original game by featuring a daytime segment focused on social interactions and a nighttime segment involving dungeon exploration.
At night, when the members of S.E.E.S. go to sleep, they are transported into the "Nightmare Hour," a concept similar to the Dark Hour featured in the main series. During this time, they must venture through a dungeon resembling Tartarus known as Oneiros, which is accessed through a hollow opening within a massive tree. As they explore Oneiros, the group regularly faces Arche-Persona bosses every 20 floors. The identities of the first two bosses depend on which characters the player has in their party when reaching those specific floors. The stats of these initial two bosses are fixed and do not change with progression. Nevertheless, Fuuka and the Protagonist's Arche-Personas are guaranteed encounters on the 60th and 80th floors, respectively.