Χ3

χ3 [ex tres] (pronounced "x trace") was a feature present in the Kingdom Hearts Union χ app, accessed from the home screen. It acted as an information and community hub built around Kingdom Hearts III. It used an identical user interface to the Gummiphone present in Kingdom Hearts III and shared many of the same functions, such as the ability to play a few select Classic Kingdom minigames. It was added on September 3, 2018.

Official Site
An icon that directly opened the default mobile browser and links to the official Kingdom Hearts website.

Official Twitter
Similar in function to the Official Site icon, it opened a browser and links to the Kingdom Hearts Union χ[Cross] ' s Twitter account.

The Road to KH III
An icon that would have redirected to a special webpage that featured a special Kingdom Hearts III video leading up to the game's release. The webpage was never completed and it only displayed a "Coming Soon!" screen.

Community
An interactive bulletin board system (BBS) that allowed players to discuss and chat all things Kingdom Hearts. The various subforums include: "Talk about Kingdom Hearts", "Strategies", "General Discussion", and "Party Recruitment."

Classic Kingdom
A small selection of Classic Kingdom games were made available for players to try out before Kingdom Hearts III's release. These included: Fishin' Frenzy, Giantland, The Musical Farmer, The Karnival Kid, and The Barnyard Battle. They utilized simple touch controls meant to emulate old handheld LCD game systems. Receiving a high score in all five games gifted players with a redemption code (for the console of their choice) to acquire the Starlight Keyblade as soon as they begin Kingdom Hearts III.

Settings
Players could configure background music and sound effect settings via this option.

Home
Tapping this icon returned the game to the Kingdom Hearts Union χ home screen.