The following opening and tutorial is required on a player's first playthrough, but can be skipped on subsequent playthroughs.
Kingdom Hearts Birth by Sleep begins on Destiny Islands, where a young silver-haired man watches over the sunset. He muses that this world is just too small.
Decades later, the now elderly man returns to the islands with a blond-haired boy in a white bundle, whom he intends to live out his final moments. Meanwhile, the boy's heart comes in contact with that of a newborn, who senses that his heart is broken and offers to bond with it. As the two accept, back in the waking world, the boy summons a Keyblade, much to the elderly man's surprise.
Four years later, the boy, a Keyblade apprentice named Ventus (Ven for short), awakens to a meteor shower. He rushes out of his room to a cliff on the side, doing some training in the process, but nods to sleep shortly after. However, he is roused by his friends Aqua and Terra, fellow Keyblade apprentices who are about to have their Mark of Mastery exam the next day. After a brief sparring match, Aqua offers her friends Wayfinders, good-luck charms fashioned after paopu fruits from the Destiny Islands with magic imbued.
Meanwhile at the Mysterious Tower, King Mickey rides on a book over waves of water, but is sucked down a whirlpool. He reappears in the office of his master Yen Sid, who feels that something horrible is about to transpire.
At this point (or if the player skipped the tutorial), the player can choose their character in a Dive to the Heart. The recommended order to play the first three storylines is the following: first Terra, then Ventus, and finally Aqua.
The next day is the Mark of Mastery exam. Administering the exam are Keyblade Masters Eraqus and Xehanort, the former being the apprentices' master and the latter being the elderly man from the opening scene. As Ven watches from the sidelines, Eraqus begins Terra and Aqua's exam by challenging them with orbs of light. Xehanort slyly imbues the orbs with darkness, forcing Ven to join in, but the exam comes to pass. Up next is a duel between Aqua and Terra. As they fight, Terra briefly taps into the darkness, which results in him failing the exam while Aqua passes.
Xehanort leaves the room and enters a secret corridor where a masked boy awaits. The masked boy believes that Ventus is too weak and needs incentive to leave the Land of Departure.
Disappointed in himself, Terra sits outside, lamenting his failure. Xehanort steps outside and tells Terra that darkness, despite Eraqus's teachings, cannot be destroyed, only channeled, before leaving.
Eraqus soon calls an emergency meeting with Aqua and Terra. The two apprentices are assigned to venture out into the worlds to subdue the Unversed, negative emotions taken form as monsters, and to search for Xehanort. Terra takes it as a chance to prove himself worthy of the Mark of Mastery.
Meanwhile, in his room, Ventus is confronted by the masked boy, who warns Ven to hurry lest Terra will be gone forever. Though Ven asserts that Terra is his friend, the masked boy mocks him, convincing Ven to chase after Terra. As Terra prepares to leave on his mission, Ven catches up to him and attempts to warn him, but Terra soon leaves, forcing Ven to pursue Terra. Eraqus, shocked at Ven's departure, orders Aqua to follow Ven and keep an eye on Terra.
And so, the three Keyblade apprentices set off on their own quests...
Tropes:
- A Minor Kidroduction: Xehanort is introduced as a youth on Destiny Islands, musing on how small the world is, before the scene shifts to him as an elderly man.
- Call-Forward:
- Xehanort's introduction harkens back to his future Heartless, Ansem:
Ansem: "Take a look at this tiny place. To the heart seeking freedom this island is a prison surrounded by water. And so this boy sought out to escape from his prison. He sought a way to cross over into other worlds. And he opened his heart to darkness."
Young Xehanort: "This world... is just too small."- Aqua's introduction, where Ven wakes up and sees her looking down on him, is almost completely identical to Kairi's in the first game, complete with Ven saying, "Give me a break, Aqua!" much like how Sora says, "Give me a break, Kairi!"
- Failed a Spot Check: While Eraqus notices the orbs tainted with darkness, he doesn't realize Xehanortnote is responsible.
- Forced Tutorial: The tutorial is required the first time around. Not so much on subsequent playthroughs.
