A prequel to Kingdom Hearts 1, Kingdom Hearts: Birth by Sleep puts players in control of Terra, Ventus, or Aqua. Each character with his/her own story to play through. All three characters training to be Keyblade Masters, they have to take their Mark of Mastery Exams, however, things go wrong when a mysterious boy and his master appear to fulfill their hidden agenda.
Terra is the oldest of the three protagonists and he acts like the older brother of the three. Terra is always trying to protect Ventus from any danger that may come his way. Terra's biggest challenge throughout the game is fighting the darkness in his heart.
Aqua is responsible for making sure Terra doesn't fall into darkness. She was given this mission by Master Eraqus after he saw Terra having problems with the darkness in his heart.
Ventus is the youngest of the three protagonists and he is a very kind hearted person. After finding out that Terra may be in trouble, he left his world following Terra to try and protect him. Ventus' existence is a very important part of the story in the game.
Land of Departure is the home to three protagonists. They grew up together in this world and have trained here to become Keyblade Masters and protect the rest of the worlds.
Enchanted Dominion is based on the 1959 Disney film Sleeping Beauty. This is the home to the villain Maleficent.
Castle of Dreams is based on the 1950 Disney film Cinderella. This is one of the first worlds the protagonists visit after leaving Land of Departure.
Dwarf Woodlands is based on the 1937 Disney film Snow White and the Seven Dwarfs. This is one of the first worlds the protagonists visit after leaving Land of Departure.
Radiant Garden is the home to many of the Final Fantasy characters in the game. In Kingdom Hearts 1, Kingdom Hearts: Chain of Memories, and the first part of Kingdom Hearts II, this world is called Hollow Bastion.
Disney Town can also be called the "minigames world" since the main objectives for the protagonists is to play minigames. This world is the home to many iconic Disney characters such as Minnie, Chip & Dale, Daisy, etc.
Olympus Coliseum is based on the 1997 Disney film Hercules. Olympus Coliseum has been featured in many Kingdom Hearts games. Zack from Crisis Core: Final Fantasy VII is introduced for the first time in this world.
Deep Space is based on the 2002 Disney Film Lilo & Stitch . This is where Experiment 626 (Stitch) is introduced for the first time.
Neverland is based on the 1953 Disney Film Peter Pan. Different parts of the world have been introduced in each game. In Kingdom Hearts: Birth by Sleep, the protagonists, fight while being on the island.
Mysterious Tower is the home of Keyblade Master Yen Sid. Yen Sid is known for teaching King Mickey everything he knows. This is one of the last worlds the protagonists visit throughout the course of his/her story.
Keyblade Graveyard is where the big showdown happens. The fight between the protagonists and Maxter Xehanort with the mysterious masked boy.