The Lingering Will is the lost mind of Terra when he defeats Xehanort in the end of the kingdom hearts birth by sleep.
Kingdom Hearts Birth by Sleep
Just as Master Xehanort possesses Terra's body and transforms him into the new Xehanort, Terra's mind finds residence in his discarded armor and brings it to life as the Lingering Will. The Lingering Will, determined to stop Master Xehanort at all costs, creates a giant force field, the Will's Cage, to trap Terra-Xehanort. Angered by Terra's defiance, Terra-Xehanort engages the Lingering Will in battle.
In the end, the Lingering Will emerges victorious, knocking Terra-Xehanort unconscious. The armored figure then thrusts its Keyblade into the ground, kneeling down. Soon after, Terra-Xehanort is consumed by an immense sphere of light, the result of Aqua and Ventus destroying the χ-blade following Vanitas's own destruction. The clouds overhead then cover Kingdom Hearts, disappearing above, leaving the Lingering Will to remain alone in the Keyblade Graveyard, silently promising to Aqua and Ven that someday, it will set things right.
Kingdom Hearts II Final Mix
Eleven years later, a portal to the Badlands in the Keyblade Graveyard mysteriously appears in Disney Castle. Sora, Donald, and Goofy proceed to enter the portal and find the Lingering Will in the same position as it had been left in. It mentions Aqua, Ventus, and the Keyblade. It then mistakes Sora as "the one he had chosen"; realizing its mistake, it asks why he isn't "him".
Then it wonders if Sora is Xehanort, slowly pronouncing the latter's name, before finally rising up as it did once before to attack him. Sora fights back and wins the battle, and the Lingering Will merely kneels down again after this. Sora can return for rematches against the Will, which agrees to fight, but it is unknown if the subsequent rematches are canon.
As the Lingering Will is truly an inanimate object, it cannot feel or possess a personality of its own. Since it was brought to life by Terra's discarded thoughts and emotions, however, it is able to "feel" a strong hatred towards Xehanort, a close connection and devotion to Aqua and Ventus, and a familiarity with Riku and Sora.
- The only two people the Lingering Will has ever fought are Sora and Xehanort, the series' main protagonist and antagonist, respectively.
- The Lingering Will is the only character in the series so far whose theme, "Rage Awakened", plays when one fights against it and plays as it.
- The Lingering Will is erroneously described as "a man covered in armor" in Jiminy's Journal in Kingdom Hearts II Final Mix, although it is actually Terra's hollow armor.