Sora-Heartless

Sora's Heartless is the Heartless of Sora, and serves as a minor character of Kingdom Hearts and major character 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 his 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, The Journal revealed to Data Sora that Sora's Heartless is the source of all Bug Block corruption 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 friend's 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 gained his powers 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 any Hearts, but the minds of the Heartless and they were absorbed into Sora's Heartless. While he absorbed the Heartless, his power span out of control, and it was about to enter the real world. When Data Sora fights Sora's Heartless, it changes his shape and becomes a dark shadow shaped Sora. When Sora's Heartless was about to win the fight, King Mickey appears and helps Data Sora defeat it.

Personality
His personality is that of a Heartless that only thinks of devouring hearts. He also had the collective minds of data Heartless that was slayed by the Data Sora.

Appearance
In Kingdom Hearts he looks like a regular Shadow Heartless. In Kingdom Hearts coded he can change form to a Darkside, Sora's size to become Shadow Sora, and a Shadow.

Playing As Sora's Heartless in Kingdom Hearts
Sora turned into a Shadow Heartless after his second fight with Riku. He is only in this form briefly and can only jump and run around. (If the Start button is pressed when Sora is in this form, Sora's menu cannot be accessed.) However, due to Kairi's heart, he was able to recover into his human form again.

Trivia

 * In Kingdom Hearts (game) as a Shadow Heartless, Sora is unable to activate any of the lift nodes to bring him back to the ground floor, and has to rely on jumping off the sides of the building. However, if he jumps too far and lands in the ravine below, the lift node activates to bring him back to ground level.
 * Sora stated to Kairi that while a Heartless, he nearly forgot everything.
 * The reason Sora became a normal shadow is because his heart doesn't have that much darkness in it.
 * In the Kingdom Hearts manga Kairi says she is able to tell him apart from the other Shadow Heartless, because she can feel that it's him and the way the calves are shaped.
 * It is confirmed by Tetsuya Nomura that this event triggered a side effect and created the Anti Form when Sora was given his new clothes and Drive Form abilities a year later.