Body
Thebody (肉体, nikutai?) is a recurring factor and philosophy in theKingdom Hearts series; along with theheart andsoul, it is a part vital to the complete existence of any living thing. The body gives the heart and soul a vessel, granting a person a physical appearance and form. The body is a medium for a person's heart and feelings to be expressed in the physical world.
The heart controls the body, much like the brain in the real world, so when someone becomes aHeartless or otherwise loses their heart, their body and soul usually wither away to nil. However, if that person's heart is strong enough, their soul will take control of the now empty body, which will start to act on its own, becoming a being called a "Nobody."
While the heart is the deciding factor as to whether or not a person can wield theKeyblade, the body can be used in a loophole for acquiring the Keyblade, as seen withAnsem, Seeker of Darkness andRiku inKingdom Hearts. Ansem possesses Riku's body, thereby controlling his heart and giving him access to Riku's Keyblade-wielding powers.
Should aKeyblade wielder discard their body to transfer their heart into a new vessel, it vanishes from existence. It will return after the destruction of the Heartless and Nobody that comes from the vessel, as is the case forXehanort. Because he wasn't able to absorbTerra's heart into his own, Xehanort is revived as his older self, instead of asTerra-Xehanort, the body that actually split intoAnsem andXemnas. Through unknown means,Luxu can completely dominate his new host, making the body his own permanently.
