Subject X is a mysterious, fifteen-year-old girl who appeared in Radiant Garden sometime before it’s fall at the hands of Terra-Xehanort. Her true identity is unknown.
Story[edit | edit source]
Between Kingdom Hearts Birth by Sleep and Kingdom Hearts[edit | edit source]
Sometime after Xehanort became an apprentice to Ansem the Wise and before he and the other apprentices exiled Ansem, Subject X appeared in Radiant Garden, shortly before dawn one day. She was found with no memories, other than that of four friends and a key, and the phrase "May your heart be your guiding key." Intrigued by her lack of memories, and thus being able to relate to her, Xehanort began to attempt to investigate her and her heart, hoping to find a way to access her memories from there. While imprisoned as part of the experiments of the heart, she was found by both Lea and Isa, who had been trying to break into the castle, curious what was inside. The two hoped to help break her out, and regularly returned to visit her. However, Ansem the Wise found out about the experiments, and ordered all those who had been experimented on to be freed. During this time, Braig took Subject X.
Her sudden disappearance prompted Xehanort to begin experimenting on his own heart and memories, believing Ansem the Wise had hidden her, while Lea and Isa decided to become apprentices to Ansem the Wise when they suddenly could not find their new friend.
After Ansem is exiled by Xehanort and Organization XIII is formed, now Nobodies, Axel and Saïx work to make their way up the Organization's ranks, hoping to get Saïx close enough to Xemnas in order to find the missing girl.
Kingdom Hearts III[edit | edit source]
Ansem, Seeker of Darkness finds Ansem the Wise in the Dark Margin with Aqua, and takes him, demanding to know where Subject X is. However, Ansem has no knowledge of the girl's location.
Later, the day before the Keyblade War, Saïx confronts a since-recompleted Lea about having abandoned him and the missing girl in favor of Roxas and Xion, though Lea insists he never forgot about Subject X.
Subject X's location and fate remain unknown.