Time Travel

Time travel is a person or object's movement away from the present time and to a different point in time in the past or the future. It is used by multiple characters in the series, particularly various incarnations of Xehanort in order to fulfill their purposes of starting a second Keyblade War.

The Methods of Travel

For someone to move through time, they must first abandon their body, becoming nothing more than a disembodied heart in the process. Xehanort accomplished this task by turning himself into a Heartless, allowing this incarnation of the man to make the travel necessary to begin the recruitment of the real Organization XIII.

The act of disembodying one's heart also allows the traveler to grant access to time travel to incarnations of themself scattered through different points of time. However, so long as these incarnations are not disembodied, they are unable to travel through time of their own accord, requiring assistance from the disembodied traveler.   

The Laws of Time Travel

In order for one to travel to a certain point in time, there must be another version of them waiting at said destination. In addition, rewriting the events that are destined to happen is forbidden in the laws of time; what is set in stone cannot be changed. Upon return to one's original point in time, the traveler loses all memory of the experience gained traveling. In spite of this, the memories of these experiences are etched into the traveler's heart, which can potentially have an effect on their perspectives and decisions. 

Characters Who Have Time Traveled

Terra-Xehanort

Terra-Xehanort, the one who started Xehanort's journey through time.

Terra-Xehanort is the body of Keyblade apprentice Terra possessed by the heart of Master Xehanort. During his apprenticeship under Ansem the Wise, he takes the opportunity provided by Ansem's trust and resources to further study the darkness and find potential ways to gain further access to its powers. Upon banishing Ansem to the Realm of Nothingness, he takes his former master's name and falsely assumes his identity, then proceeding to separate his heart from his body, splitting himself into a Heartless and a Nobody: Ansem, Seeker of Darkness, and Xemnas, the leader of Organization XIII.

Ansem, Seeker of Darkness

The form Ansem initially had upon starting his journey through time.

Ansem's function as a Heartless, a disembodied heart corrupted by darkness, enabled him to travel through time, just as Xehanort planned when he cast off his heart to create the former incarnation. Using this ability, he travels to the past and arrives on his original self's former home world, Destiny Islands, to convene with a younger version of himself. With time travel powers granted to him and the rest of his incarnations by Ansem, Young Xehanort is able to travel through time without leaving his body behind. His task fulfilled, Ansem returns to his own time and places himself on Destiny Islands, where he places the Recusant's Sigil on a time traveling Sora.

Ansem later possesses Riku, reshaping Riku's body into a physical form designed in his image. 

The form Ansem molds for himself via his possession of Riku.

Young Xehanort

Young Xehanort used time travel to gather the True Organization XIII.

With the ability to travel through time granted to him by Ansem, Young Xehanort uses his newfound power to visit dispersed versions and vessels of himself in many points in time. Able to gather ten of these individuals, he gathers them in the present day to join Xehanort's True Organization XIII. The currently known incarnations who have been gathered are Ansem, Xemnas, Xigbar, and Saix, all of whom were defeated by Sora and Riku in the present day.

In addition to this, when placed on Destiny Islands by Ansem during a time before it was destroyed by the Heartless, he is able to follow Sora and Riku into the Realm of Sleep. With Sora marked by the Recusant's Sigil and Young Xehanort present in the same time period as him, the youngest incarnation of Xehanort is able to keep tabs on him wherever he might be. This allows him to track Sora wherever he goes as part of his assigned task to turn him into the thirteenth vessel for the True Organization XIII.