This is an enhanced version of Persona 3. In addition to all the content from the original game, it adds an entire playable epilogue starring Aigis as the player character. This consists of a huge new dungeon called the "Abyss of Time", and clarifies several lingering plot threads from the conclusion of the original game. "The Journey" is the name given to the main story of the original game in this version, whilst the playable epilogue dungeon is called "The Answer" and can be accessed from the main menu at any time.
It also adds a number of less obvious changes and additional content, which can be found scattered throughout the original game's story. This includes the ability to take Koromaru on walks to gain random items or get a boost to a Social Link, the ability to view secret videos of the protagonist's dorm mates from the control room, the addition of a hard mode, and a number of new quests to complete. It also overhauls the Naganaki Shrine, allowing players to use it to alter various properties of Tartarus for their next visit, adds several new fusable Personas, adds an extra scene involving a certain character, and adds new wearable costumes. It also makes some other balance and gameplay adjustments, mainly involving Persona stats, skillsets, and when certain Social Links can be accessed. FES is an abbreviation for festival a common term in Japan.