Ansem's Code

Ansem's Code is a Code Ansem the Wise hid inside Sora's heart, after Roxas returned to Sora and before Sora awakens.

One of the subjects inside the data is about the three compartmentalized "boxes" inside Sora, each one containing the heart of another person: one box holds Roxas's heart; another one holds Xion's heart, and the third one, which has been with Sora for a much longer time, holds Ventus's heart. These three hearts have melded with Sora's and no longer have voices of their own; as such, attempting to manually extract them from Sora's heart can be just as deadly as becoming a Heartless.