Kingdom Hearts Union χ[Cross], previously titled Kingdom Hearts Unchained χ, is a Kingdom Hearts game exclusive to the iOS and Android smartphone platforms as the eleventh game of the series. It features plot and gameplay elements from the Japan-exclusive web browser game Kingdom Hearts χ[chi] and is free to play, though it includes in-app purchases. It is the first Kingdom Hearts game to be released on smartphone platforms. Kingdom Hearts Unchained χ was first announced on May 12, 2015. During Square Enix's E3 Conference on June 16, 2015, a trailer for the game was released showcasing gameplay. Kingdom Hearts Unchained χ was released in Japan on September 3, 2015, and in North America on April 7, 2016. In April 2017, the game was rebranded with the Kingdom Hearts Union χ[Cross] content update, featuring multiplayer and a theater mode. In September 2015, Square Enix announced a new game entitled Kingdom Hearts HD 2.8 Final Chapter Prologue. The collection features Kingdom Hearts χ Back Cover, a 60-minute cinematic film that focuses on the Foretellers, elaborating on their actions during the game's events and their attempts to determine which of them is the traitor. It was released in January 2017.