Sora's Heartless

Sora's Heartless is a form that Sora takes from the final act of Kingdom Hearts, through Kingdom Hearts: Chain of Memories, and ending with the first act of Kingdom Hearts II. This event was recorded within Jiminy's Journal, and when that record was magically manipulated by Naminé, and then digitized by King Mickey in Kingdom Hearts coded, the digital version of the Heartless gained new, malevolent life, and proceeded to cause the Bug Block corruption.

Kingdom Hearts
After Sora, Donald, and Goofy track Riku down to the Great Hall, they learn that he has used the incomplete Keyblade of People's Hearts to summon the Keyhole of Hollow Bastion. He reveals that Kairi's lost heart has been within Sora all along, and that it must be released in order to complete the Keyhole. He moves to release Kairi's heart by using the Keyblade on Sora, but Sora parries at the last second, and eventually defeats Riku.

Despite this, Kairi is still catatonic, and Sora is unable to seal the incomplete Keyhole. In order to save Kairi, Sora turns Riku's Keyblade on himself. This releases Kairi's heart from Sora, reviving her, but also completes the Keyhole and casts Sora into darkness, transforming him into a Heartless, and releasing his Nobody, Roxas, as well as Kairi's Nobody, Naminé. Sora fades into a Shadow just as Kairi awakens, and the Heartless rapidly emerging from the Keyhole force Kairi, Donald, and Goofy to flee. As a Shadow, Sora follows his friends through the Lift Stop to the Entrance Hall, where he sees them being overrun by other Shadow Heartless. He rushes to help his friends, and though Donald tries to attack him, Kairi recognizes him and embraces him (in the manga, Kairi jokes that she recognized Sora's Heartless by the shape of its calves). Her light returns Sora to his human form, and Sora later states that while a Shadow, he nearly forgot everything. Sora remains a pseudo-Heartless throughout his battle with Ansem, Seeker of Darkness.

Kingdom Hearts: Chain of Memories
Sora's Heartless was only mentioned by Goofy when he was worried when Sora becomes a Heartless. As Naminé was partially created from Sora when he became Sora's Heartless, she was able to manipulate his and his friend's memories, and Organization XIII forced her to do this in order to brainwash Sora at Castle Oblivion. After Naminé puts Sora to sleep, she blanks the contents of Jiminy's Journal in their time in Castle Oblivion, as well as Sora and his friend's memories, and then begins restoring them. However, while the memories were reconnected, the Journal itself remained blank. This is later revealed to be due to the record of Sora's Heartless beginning to assert itself.

Kingdom Hearts II
One year later, the Replica of Sora's Nobody, Xion, is reunited with his Nobody, Roxas, and the pivotal event at Hollow Bastion later appears within Roxas's final dream-memories. Finally, Roxas is reunited with Sora, and Sora reawakens as a complete being, no longer a Heartless. Although he was whole, his time as a Heartless and the magic of his new clothes allowed him to infrequently assume a Heartless-based Anti Form.

Kingdom Hearts coded
After clearing the Bug Block from the data Hollow Bastion, the Journal reveals to Data Sora that the digitized version of Sora's Heartless was the source of the Bug Blocks corrupting the Journal. While Data Sora had been exploring the Data Worlds and gained new power, the digitized Sora's Heartless was corrupting the other data, changing them to make itself stronger. Data Sora attacked the digitized Sora's Heartless, but instead of releasing hearts it released the minds of slain Heartless, which it reabsorbed, increasing its power exponentially. Data Sora attacked it again as it took the form of AntiSora, and just as the Heartless was about to win the fight, King Mickey appeared and helped Data Sora slay it.

Appearance
In Kingdom Hearts, Sora's Heartless originally appeared as a Shadow, but regained its form as Sora when Kairi recognized it.

In Kingdom Hearts coded at the Data World, Sora's Heartless appeared first as a Darkside, then as an AntiSora, and finally as a Shadow.

Gameplay
In his Shadow form, Sora can only jump and run. He can no longer activate lift nodes or the pause menu, and unlike other Shadows, he cannot perform a lunge attack. However, if Sora falls too far in the Lift Stop, a lift node will automatically activate to bring him back up to the correct floor.