The Thieves Guild, otherwise knows as the Thief's Union (怪盗同盟, Kaitō dōmei)? in the Japanese version, is an online feature in Persona 5 that requires an Internet connection. It is accessed by touching the controller's touchpad when available in the PlayStation 4 version, and "select" in the PlayStation 3 version.
Persona 5 / Royal
The Thieves Guild is a service that provides many online features to players. It allows them to check what activities other players have done on their in-game day, as well as the entire player base's average level for that date. Additionally, when asked a question in class, they can view what answers other people have chosen, tallied in a poll; that way, the player can check the correct answer for themselves in advance, as it should have won the majority vote by a landslide. However, this feature can not be used during exams.
The Thieves Guild also offers services during dungeon exploration as well, although it can only be used up to three times per dungeon visit (or an in-game day). A Downed ally may be taken hostage by an enemy, and the protagonist has to negotiate in order to free them. With the Thieves Guild, the negotiation process can be skipped. After a set amount of time has passed during battle in a Palace, an enemy will try to run away, which will increase the Security Level. By making use of the Thieves Guild, the enemy is prevented from running away. In those cases, as the name of the Phantom Thieves of Hearts can be customized (only once per playthrough), it will also be displayed to other players.