Four years before Aqua and Terra take their Mark of Mastery exam, Ventus served as an apprentice to Master Xehanort, as part of the elderly Keyblade Master's plans to forge the legendary χ-blade. However, Ventus proved to be a poor candidate, and when he refused to use his darkness to fight several Neoshadow Heartless in the Keyblade Graveyard, Master Xehanort finally lost patience with him and used his own Keyblade to unlock and extract the darkness from Ventus's heart, using it to form a being of pure darkness who is then named "Vanitas" by Master Xehanort.
Unfortunately, the process left Ventus in a comatose state, with his broken heart of pure light slowly fading out of existence. Master Xehanort, disguised in a Black Coat, then took Ventus to Destiny Islands to allow him to live out his last days peacefully. Ventus is sent to the Dive to the Heart, where he comes in contact with the heart of a young Sora. After a brief discussion, Ventus's heart connects with Sora's, mending his broken heart and allowing Ven to stay alive until he someday becomes strong enough to repair the damage by himself. Ventus then summons a Keyblade, much to Master Xehanort's surprise.
Following these events, Xehanort brought Ventus to Land of Departure, where he could train as an apprentice to Master Eraqus. Terra and Aqua met Ventus with open arms. However, when Terra asked Ventus about his past, he screamed out in agony, eventually falling unconscious. Eraqus revealed that this was because Ven had lost his memories. Afterwards, he remained asleep for some time. As he slept, Aqua kept watch over him, to keep him safe. Some time later, Ven woke up. Overjoyed, Aqua quickly alerted Eraqus and a worried Terra about Ven's recovery.
It was then that his heart began to heal and he started to form strong bonds of friendship with Terra and Aqua. During a training session, Ventus loses humiliatingly, but Terra and Aqua reassure Ven that he was getting stronger. As time went on, Terra and Ven grew close, forming a brotherly bond. Terra even went so far as to give Ven his wooden training Keyblade and recite a mock inheritance ceremony. Together, the three of them shared the same dream: to become Keyblade Masters.
Years later, Ventus awakes to a meteor shower and hurries out to look at the stars. Later, both Terra and Aqua join him. When Ven asks about stars and their light, Terra explains how each star is another world and compares the light to Ven, who doesn't understand. After a brief spat between the two boys, they, along with Aqua, spar in order to prepare for the Mark of Mastery exam the next day. Following their workout, Aqua gives both Ven and Terra good luck charms and tells them the story behind the charms. The charms, also known as Wayfinders, were gifted with a powerful magic that formed an "unbreakable connection". Upon receiving the charms, Ven and his friends return to their castle for the night, eagerly awaiting the exam.
However, things don't go smoothly. During the exam, Master Xehanort rigs the test, and the orbs of light attack Ven and his friends. Together, the three fight off the orbs, and the exam continues.
After the exam, it's clear that Ventus has earned the interest of Master Xehanort and his apprentice, Vanitas. Though their intentions are rather ambiguous at the time, Vanitas decides to give Ventus some incentive to leave his home. When Vanitas appears in Ven's room, he leaves dark hints of Terra's fate and how he'll "become a different person". Ven becomes very defensive, telling Vanitas that he doesn't know the first thing about Terra. However, once Vanitas leaves, via a Corridor of Darkness, Ven hurries out to find his friend in hopes of giving him a warning.
Unfortunately, Ven arrives much too late, as Terra leaves to go on his mission. Left with no other choice, Ventus leaves his home and begins a journey of his own.
He visits a number of worlds and builds new friendships along the way. In the Dwarf Woodlands, he helps Snow White escape the woods and guides her to the Dwarfs' home. There, he learns that Snow White encountered Terra and immediately tries to get to the bottom of things. After facing several more Unversed along the way, Ven encounters the Queen in the form of an old lady, and she tells Ven that Terra threatened her with his Keyblade. Refusing to believe this, Ventus leaves in hopes of finding Terra, wondering what's gotten into him.
Then, in the Castle of Dreams, Ven befriends Jaq and Cinderella. Though Terra isn't there, Ven still lends a hand, helping gather supplies for Cinderella's dress, and even facing Lucifer. When the dress is complete, Cinderella thanks Jaq and Ventus, and the two talk about their dreams. It's here that Ven decides that his dream is to become a Keyblade Master; the dream he and his friends all share.
It's in Enchanted Dominion that Ven gets another clue regarding Terra. After freeing Princess Aurora's heart, Ven encounters Maleficent. Maleficent reveals that Terra helped steal Aurora's heart, but Aqua arrives just in time to convince Ven otherwise. She then asks Ven to go home with her, but he refuses, remembering the cryptic warning left by Vanitas.
Coincidentally, Ven encounters Vanitas again after leaving Enchanted Dominion, and he follows him straight to the Keyblade Graveyard. There, Ven tries to get some answers out of Vanitas, who simply restates what he said before, that Terra will be gone forever. The two battle, but Vanitas easily outmatches Ven and nearly kills him. It's not until King Mickey arrives, that Vanitas is defeated. Upon his defeat, Vanitas tells Ventus that he's on probation and disappears, leaving Ven and Mickey alone. 
The two introduce themselves to one another, and Mickey tells Ven about the Star Shard. Apparently, it allows him to travel to different worlds, but he still doesn't know all of its secrets. Shortly after, the Star Shard sends the two of them both to Radiant Garden, and Ven tries to follow Mickey, only to be intercepted by Aeleus and Dilan. After spying an Unversed, Ven gives up his search for Mickey and instead trails after the monster. He's interrupted several times, by Scrooge McDuck, who gives him lifetime passes to Disney Town, and Merlin, who tells him of the book to the 100 Acre Wood.
Eventually, he does find the Unversed he was chasing, as well as Terra and Aqua. Together, they face the Trinity Armor, but after its defeat, things change for the worse.
First, Aqua tries to tell Ven to go home, and then she and Terra get into a fight regarding the darkness and Eraqus's intentions. The whole time, Ven is left completely confused, as he'd never seen his friends bicker in such a way. In the end, he tells Aqua that she's let being a Master go to her head, and he leaves to find Terra again.
His search is interrupted again, when he spots Ienzo being attacked by the Unversed. Without any hesitation, Ventus protects the boy and defeats his attackers. Even arrives shortly after and thanks Ventus for his help. Then, when asked about Terra's location, he tells Ven to look in the Outer Gardens.
Though Ven does find Terra, their reunion is short lived, as Terra leaves, telling Ven that he can't come along, but when he really needs Ven, he knows Ven will be there. Meeting up with Aqua again, Ven asks to come along, but Aqua orders him to return to the Land of Departure in a somewhat harsh manner. Seeing Ven's disappointment, Aqua softens and explains that she merely doesn't want him to get hurt before departing.
For a while, Ven stays in Radiant Garden, reminiscing about the times when his friendship wasn't strained by newfound complications. He's left wondering just what it means to be friends, and after meeting Lea and Isa he becomes more and more curious about friendship.
Thus, when he continues his travels, Ven has a new resolve. Rather than search for Terra and Aqua, he decides to go out and make some new friends in hopes of redefining his simplistic views of friendship.
By the time he leaves Olympus Coliseum, Ven finally comes to understand what it means to be friends and realizes that he, Terra, and Aqua will patch things up someday.
Later, in Neverland he finds Mickey's Star Shard, only for Captain Hook to steal both it and Tinker Bell. Together, both he and Peter Pan team up against the pirate captain, saving Tink in the process.
Together, Ventus, along with Peter and the Lost Boys, decide to put their own personal treasures in the empty chest they stole from Hook. As the Wooden Keyblade holds many cherished memories for Ven, he puts it in the chest, for his best memories with Terra and Aqua are still to come. With Hook out of the way, he also retrieves the Star Shard from Tinker Bell after a little persuasion from Peter, only to be whisked away to the Mysterious Tower.
Upon his arrival, Ven meets Donald Duck and Goofy, who take him straight to Yen Sid. There, it's discovered that Mickey went missing, but when Yen Sid uses his magic to find him, they discover that the King is in danger. Determined to save Mickey, Ven departs from the Tower and returns to the Keyblade Graveyard, but when he reaches Mickey, everything changes.
It turns out that Master Xehanort was waiting for him the whole time, and that's not all. Xehanort reveals Ven's destiny to forge the χ-blade. He tells Ven that this is the real reason why he was never allowed to leave home and constantly told to return, out of fear for the χ-blade's creation.
After learning of his past, Ventus returns to Eraqus, only for his Master to try and destroy him upon realizing Xehanort's plans. Fortunately, he is saved by Terra and sent to Destiny Islands, much to his displeasure. There, he encounters Vanitas again, who taunts him into remembering how Master Xehanort broke their heart in twain.
Once the memories return, Vanitas decides to give Ventus a reason to fight: Vanitas tells Ventus to come to the Keyblade Graveyard, the only place where the χ-blade can be forged, and threatens to kill Terra and Aqua to see if Ventus will continue to "play the pacifist." Left with no choice, Ven leaves in hopes of setting things right, once and for all. Once reunited with his friends, Ventus explains the situation between himself and Vanitas, and, admitting that he is terrified over the very thought of the χ-blade, asks to be destroyed in the event that he does have to fight Vanitas, much to their shock. However, there's little time to mull over Ven's request, as both Master Xehanort and Vanitas arrive.
During their final battle at the Keyblade Graveyard, Master Xehanort encases Ven in ice and throws him off a cliff. Aqua manages to catch him before he hits the ground. Braig quickly appears and fights Aqua. Stalling long enough, Braig withdraws from the battle. Vanitas knocks out Aqua as he drops down from a cliff. He prepares to kill Aqua, but before he can, however, Ven uses all his willpower to thaw himself and defend his friend. After the battle, Vanitas reveals his true intentions and explains that the Unversed came from his negative emotions. Trapping Ven with several Floods, Vanitas merges with Ventus and gains control over his body.
However, Vanitas is defeated by Aqua and Mickey, and right as the χ-blade is damaged by their fight, Vanitas and Ventus engage in a metaphysical battle, where Vanitas tries to rejoin with Ventus and repair the χ-blade. Ven, however, refuses and chooses to defeat Vanitas and destroy the weapon, even if it means the destruction of his own heart.
The two engage in a decisive battle, and towards the end, Vanitas forces a D-Link on Ventus in hopes of completing their fusion. However, Ventus prevails, and the χ-blade is destroyed along with Vanitas. Unfortunately, this also results in Ventus losing his heart, leaving him in a comatose state. Aqua later places his body in a chamber within Castle Oblivion. Somehow, Ventus's heart finds its way to a young Sora, in his own Awakening, and his heart passes on into Sora's body.