Illusory Urahara, located in the vicinity of a shrine in Harajuku, is the only purely optional Idolasphere in the game. Rather than a dungeon, it is an arena where the player can earn rewards by taking part in series of battles. Arena battles come in four difficulties: Beginner, Intermediate, Advanced, and the Legendary, the last of which only becomes available when playing on a New Game+ save. One round in the arena consists of five consecutive battles against Mirages without a break. If the player wins against all five groups of enemies, the option is given to continue with encore performances against a second and then a third set of five enemy waves; each encore triples the arena coins rewarded. The arena also offers a daily challenge battle; a special fight that can be challenged once per day.
Additional rules of the arena include:
- The player cannot swap active party members out during arena battles.
- The player cannot use any items during arena battles.
- Losing in the arena is the same as losing in a standard battle and will result in a Game Over.
- The player can attempt to run from battle at any time at the cost of forfeiting any arena coins they would have earned. As with fleeing battles in other parts of the game, any earned EXP, weapon experience, and money from sessions is still awarded.
In addition to the battles held at the arena, as the player progresses through the game they have the opportunity to 'scout' several Mirage NPCs from within the other Idoloaspheres as part of a sidequest issued by the Mirage who runs the arena. Scouted mirages will appear within Illusory Urahara and the player will be given the chance to trade their consumable items and Performa for other Performa in a sequence similar to the Demon Negotiation mechanic from ATLUS' flagship RPG series, Shin Megami Tensei.
Aside from being a location where the player can test their skills and grind weapon mastery and EXP, the Urahara Arena is notable for being the only source of the 'War Testament Perfoma needed to create each character's strongest Carnage, the only infinite source of Master Seals and Incense, as well as a few accessories that cannot be acquired anywhere else.
Nieg, the first scoutable Mirage, will give you a Incense of your choice (aside from Luck Incenses, which can be obtained as one of the random bonus Incenses he awards every 10 trades) in exchange for 9 Detritus in lieu of the ability to trade for Performa. After trading for 12 or more Incenses within a single playthrough, he will leave the arena as part of a brief side quest that culminates in the player obtaining the Perfoma needed to create the Radiant Skill Locktouch, and after trading for 36 or more Incenses on a single New Game+ playthrough the player can initiate a sidequest where they fight the game's final NG+ boss, M-DEUS.