Subject X is a mysterious girl mentioned in Kingdom Hearts III. While her true identity is not specified, she is a character who has previously appeared in the series,^[1] and is implied to be a time traveler from the age of fairytales.^[2]

Story

Before Kingdom Hearts

Sometime during Terra-Xehanort's time as a researcher working under Ansem the Wise, Subject X appears in Radiant Garden, Secret Report 3 unconscious, and is placed in a cell in the castle's laboratory. A week later she is able to speak, but she is only able to recall having four friends and a key, and the phrase "May your heart be your guiding key", despite the prodding of the researchers. Secret Report 1 Xehanort plans to probe her heart in hopes of restoring her memory, as he believes she may have traveled through time. Secret Report 3

During Lea and Isa's forays into the castle, they meet Subject X and befriend her, and plan to free her. Secret Report 6 However, Braig takes her away to an unknown location before they have the chance. Secret Report 1 Her disappearance was a factor in Ansem stopping the experiments.^[3]

After Subject X's disappearance, Lea and Isa become apprentices of Ansem the Wise, and later join Organization XIII, in order to find a lead on her location, but they are unsuccessful. Secret Report 6

Kingdom Hearts III

Ansem, Seeker of Darkness, assuming Ansem the Wise is the one who hid Subject X, interrogates him about her whereabouts to no avail. Later, Saïx and Lea reminisce on their past interactions with her and their failure to find her, and Lea reaffirms his desire to find her.

Design

Subject X is approximately 15 years old, and has black hair.^[4]

Notes and references

• Entelechy
• Characters of unknown Worlds
• Hollow Bastion/Radiant Garden
• Original characters
• Kingdom Hearts III characters