I am Xehanort from the most distant past. My future self gave me a task - to visit the splintered versions of myself in many worlds, and ensure they gathered here today.
Young Xehanort is Master Xehanort's younger self when he was a teenager. He was given the power to travel through and manipulate time itself by his future Heartless in order to assist his older self in assembling and containing his essence in thirteen different vessels.
Young Xehanort first appeared before Sora and Riku during their Mark of Mastery exam in the Sleeping Worlds. With the help of some of his other vessels, Young Xehanort was able to coax Sora into traveling to The World That Never Was, where his heart would become trapped in a deep slumber while his body would be used as the thirteenth dark vessel for the real Organization XIII. However, their plans were thwarted by Riku, King Mickey, Lea, Donald and Goofy, who were able to save Sora from the Organization's clutches. Despite this, Young Xehanort escaped with his future self and his other vessels to prepare for the future ahead.
While Sora, Donald and Goofy visited Toy Box, they encountered Young Xehanort, who was using the world's unique properties with living toys and their hearts to conduct several experiments. Despite being forced to withdraw from the world by the heroes, Young Xehanort learned that a heart can be placed in a vessel of their choosing, something that could benefit the Organization in finding their final member. He later confronts the assembled Guardians of Light at the Keyblade Graveyard, and later Sora when he attempts to save the hearts of his fallen allies from the Lich, warning Sora that misusing the power of waking for his own agendas would have a costly price to pay. During the Second Keyblade War, Young Xehanort is defeated in battle, and before fading away to return to his proper place in time, he taunts Sora one last time on his ultimate fate for misusing the power of waking.
Young Xehanort has mildly tanned skin with pointed ears, golden eyes, and silver hair; originally however, he had silver eyes and his ears weren't pointed. His hair slightly spikes and falls past his shoulders in the back. He has four bangs framing his face, similar to Terra-Xehanort’s hair when he became Ansem the Wise's apprentice.
When he lived on Destiny Islands, Young Xehanort wore the same style of white shirt similar to his future self and Heartless, a black vest with a high collar, long armbands which cover his forearms, and dark grey pants stuffed into his boots. When he acquires the power to time travel, Young Xehanort acquires a Replica body from the future in order to remain during his travels. With his heart contained within a Replica, the Replica becomes modeled after him physically, although he wears a black coat instead of his normal outfit.
In Kingdom Hearts Birth by Sleep, Young Xehanort's body is completely covered by a hooded black coat with a fairly tall and masculine build. He never speaks at any point of the game.
Young Xehanort wields many incredibly formidable abilities that makes him an extremely powerful foe to behold. He was granted the power of space-time manipulation by Ansem, which he uses to great effect; for example, he recovered from the effect of Mickey's most powerful Stop spell within mere moments, far faster than any of his comrades. He can manipulate time so precisely that he is capable of controlling time to achieve a myriad of effects while in battle, performing such feats as slowing his opponent or reversing the flow of time to regenerate health. During his battle with Riku, Young Xehanort would merge with the clock in the arena and if enough time has been given, could restore a decent amount of health by rewinding time. Like his older self, he is an extremely powerful magic user, capable of casting many of the most powerful spells available to all the protagonists of Kingdom Hearts Birth by Sleep, with the addition of being able to use Doom, and he can cast powerful fire, wind and ice spells that project fiery vortexes, summon tornadoes and fire several large ice blocks. His telekinetic prowess is capable of easily throwing around Riku and Mickey.
In every boss encounter, Young Xehanort is immune to all status effects and displays outstanding swordsmanship skills as well as great speed and agility, wielding first his dual-blades to perform many deadly attacks, also displaying proficiency with the whip and spear form the weapons can undertake by fusing them together, and later his Keyblade to quickly unleash a flurry of combos capable of trapping and quickly dealing heavy damage to Riku, with him also making effective use of his ability to transform it into a shield and whip. In Birth by Sleep, Young Xehanort is also capable of turning himself invisible and firing lasers. In Dream Drop Distance, he can enter the World of Sleep, summon Dream Eaters, open Keyholes and the Corridors of Darkness.
Young Xehanort wields two weapons that bear a striking resemblance to Xemnas's Ethereal Blades, but appear to have hilts, which many of Xemnas's blades do not, but they also resemble some clock hands or clock arrows. The blades are made of light blue energy and the black handles are somewhat reminiscent of the Terminus and Ruination Ethereal Blades. The blades can be combined into a dual-blade, and extend to be lashed out like a whip. Young Xehanort wields these weapons with a reverse grip, similar to the unorthodox way Ventus wields his Keyblade.
While not able to wield a Keyblade in his initial appearance, when he is briefly possessed by Master Xehanort while battling Riku in Where Nothing Gathers, Young Xehanort wields a Keyblade that incorporates elements of the No Name and The Gazing Eye Keyblades. By the time of Kingdom Hearts III, he now possesses the ability to wield his Keyblade without assistance, although he loses this ability temporarily when he returns back to his time until he trains to become a proper Keyblade wielder.