Persona 3 is a departure from its predecessors in that the story moves at a prescribed pace from day to day over the span of a calendar year, rather than jumping from one narrative event to another in typical console role-playing game fashion. Like in previous installments, the main character attends high school; however, in this game school activities are important in building up the Main Character's attributes. For example, studying in the library builds "Academics," drinking "Pheromone Coffee" builds "Charm", and singing Karaoke builds "Courage". Creating "Social Links" by building relationships with classmates and acquaintances is of particular importance, as the strength of each link will eventually affect the strength of the Main Character's performance in battle. This "day in the life" style of gameplay is similar to Japanese console RPGs with dating sim elements, like Harvest Moon, Azure Dreams, or Atlus' own Imodoki no Vampire: Bloody Bride.
While half of the game is dedicated to participating in a typical teenager's life (socializing, attending clubs, studying, etc.), the other half involves roguelike dungeon-crawling in Tartarus, the monster-infested labyrinthine tower that your high school transforms into at the stroke of midnight. Every few floors features a boss battle and chests full of money and items are randomly strewn throughout. The floors do not have set maps, except for the small boss floors, and are randomized each time the player visits.
The battle system is a turn-based affair, with the Main Character and his comrades using their Personas to exchange blows with their enemies. Persona 3's battles also feature a system dubbed Once More, similar to the Press Turn battle system used in other recent Shin Megami Tensei games such as Digital Devil Saga, in which the player is rewarded for exploiting enemies' elemental weaknesses. However, instead of rewarding the entire party, extra turns are given on an individual basis. If a player attacks a Shadow weak to fire with fire, it is knocked down. If all enemies are knocked down, an "All-out Attack" can be performed, where all party members rush the enemies at once, dealing massive damage in a large dust cloud as comic-book style onomatopoeia ("Bam!") appear above.
Only the protagonist is directly controllable in battle, while the numerous allies that join the party are governed by AI. The player can give the AI guidelines using preset "Tactics" like "Heal/Support" or "Full Assault", more of which are accumulated over the course of the game. These AI allies and the main character himself are subject to a physical well-being parameter which moves from "great" to "good" to "tired" or "sick" over the course of exploring Tartarus. If a player or friendly NPC is "tired" or "sick", their performance in battle drops dramatically, and is more likely to take a critical hit. Also, if one character is sick, they may also pass on the illness to other characters. Resting a night or two can restore the character's health.
In combat, the Main Character and his allies summon their Personas using a pistol-shaped device called an "Evoker" by aiming at their heads and pulling the trigger. With the aid of their Personas, the party is able to cast spells and perform special attacks (characters can also perform basic physical attacks themselves). While your allies in the game can only bring forth one Persona, the Main Character is able to gain many Personas and even change them in battle. When Personas level the player inherits its natural attributes in the form of basic stats such as strength and magic. New Personas can be acquired via a post-battle shuffle card game, or through fusion of two or more existing Persona. Here the social sim aspect of the game meets the dungeon hack portion, as the amount of bonus experience granted to a given Persona being created is determined by the strength of the Social Link with which that Persona's "Arcana" corresponds. Low-level Social Links will grant small bonuses, while higher levels give generous portions. Maxed out Social Links are required to create the most powerful Persona in each particular Arcana.