Sora's Heartless

Sora's Heartless is the Heartless of Sora, and serves as a minor appearcance of Kingdom Hearts and major appearacance in Kingdom Hearts coded.

Kingdom Hearts
Kairi was revealed to be one of the Seven Princesses of Heart, but the door to Kingdom Hearts could not open because her heart lay within Sora. In order to return her heart and wake her up, Sora used the Keyblade of People's Hearts that Riku had to remove both their hearts, sacrificing his humanity and becoming a Heartless himself. This in turn created Roxas and Naminé, the Nobodies of Sora and Kairi respectively. When he managed to reunite with Kairi after a brief stint as a Shadow, Kairi used her light to return him to his human form. Since the Heartless he turned into was a Shadow, it would seem that Sora has little darkness in his heart, as the strength of a person's Heartless is measured by the darkness in their heart.

Kingdom Hearts coded
In Episode 7 Data Riku revealed to Data Sora that Sora's Heartless is the source of all Bug Block courrption in the Data World. It turns out that in Kingdom Hearts: Chain of Memories the entire record of Jiminy's Journal, along with Sora and his friends' memories, were all erased and then restored by [Namine]]. The Chain of Memories was supposed to have been reconnected, but the notebook... The record was still erased. While Data Sora gain his power in the data world, exploring other Data worlds and gaining new power the data version of his heartless was corrupting the other data, changing it to make itself stronger. When Data Sora fought the Data Heartless in the Data world he didn't release Hearts but the minds of the Heartless and they were absorbed by Sora's Heartless. While he absorbed the Heartless his power is out of control and is about to enter to the real world. When Data Sora fight Sora's Heartless he changes his shape and becomes a dark shadow shaped Sora. WHen Sora's Heartless was about to win the fight King Mickey appears and help Data Sora.