Square Enix has announced Kingdom Hearts Unchained χ will be released in Japan via the Apple App Store & Google Play Store for iOS & Android devices respectively on September 3, 2015 at 12PM JST. That's September 2 at 8PM PST and 11PM EST. It will be available for download from 12AM JST for iOS & Android devices on the same day but the service will not commence until 12PM JST, 12 hours later.
Kingdom Hearts Unchained χ is a port of the Japan exclusive web browser game, Kingdom Hearts χ[chi] for iOS & Android devices. It is a free-to-play app with optional in-app-purchases. It has been confirmed for a release in North America.