Square Enix released Kingdom Hearts: Unchained χ and this game changed the timeline we had previously established. They’re also going to be including two new stories in the Kingdom Hearts HD 2.8 Final Chapter Prologue that will also change the timeline. Here is how it looks now with the new additions:
Kingdom Hearts: Unchained χ was released in North America for Android in April 2016. This game takes place during the Keyblade War, which means Birth by Sleep isn’t the first game in the series anymore. Then Kingdom Hearts HD 2.8 Final Chapter Prologue will bring Kingdom Hearts χ Back Cover and Kingdom Hearts 0.2: Birth by Sleep – A Fragmentary Passage. Back Cover is set to tell the tale of the Foretellers and reveal new parts of the series’ history, which leads me to believe it will take place before Unchained χ making it the first game in the timeline. A Fragmentary Passage will take place after the events of Birth by Sleep and will be told from Aqua’s perspective.