Kingdom Hearts: Birth by Sleep

Kingdom Hearts Birth by Sleep (キングダム ハーツ バース バイ スリープ) is an action role-playing game developed and published by Square Enix for the PlayStation Portable. The game was released in Japan on January 9, 2010, and is currently planned for a summer 2010 release in North America and Europe. Kingdom Hearts Birth by Sleep was also released with a limited edition PSP-3000 as a bundle in Japan featuring designs from the series on its back. Nomura has referred to the game as "Episode 0" saying that the game is on the same scale and plays as big an importance as Kingdom Hearts and Kingdom Hearts II.

The game is a prequel to the original Kingdom Hearts, taking place ten years before, and features many previously unseen characters and unexplained plot elements from the series. The game centers on the journeys of Terra, Aqua, and Ventus, characters briefly featured in Kingdom Hearts II, in their quest to locate the missing Master Xehanort. The game also utilizes an overhauled battle system different from previous games in the series with new elements such as the Command Board, Command System and Dimension Links added in.