Spirit-mortal transcendence

All beings in the world are either mortal creatures or spirits, but this distinction is not absolute. In rare cases, it is possible for a spirit to relinquish its immortality and acquire physical form to join the mortal realm, for a mortal being to transcend into the Spirit World upon death, or for both to merge into a single being.
== Forms of transcendence ==
=== Spirits becoming mortals ===
Spirits can transcend into the mortal realm by transforming into a physical, mortal body, which can be an animal or a human. While this allows the spirit to truly become a part of the physical realm, they abandon their immortality in doing so, which means they can be killed as easily as any other mortal creature. That being said, they may still remain ageless, that is to say, not die of old age.
The following spirits are known to have taken mortal form:
* Tui and La took the form of koi fish. Their motivation for doing this is unknown. While they were ageless, Tui was killed by Zhao and later revived by Yue.
* Lady Tienhai took the form of a human after falling in love with a young prince. She later died, though it is unknown if it was of old age or some other cause. Upon her human death, she became a spirit again.
=== Mortals becoming spirits ===
A mortal can either transcend as a spirit either upon death if they so choose, if special circumstances are met, or as punishment for trifling with other spirits by separating their body from their soul. Upon doing so, the mortal leaves their body behind and continues as an immortal spirit, retaining their memories and personality. Over time, however, their original personalities can change and become more detached.DiMartino, Michael Dante; Konietzko, Bryan; Dos Santos, Joaquim & Graham, Ian (July 1, 2014). "A New Spiritual Age" commentary. Book Two: Spirits Blu-ray. 
The following creatures are known to have taken spirit form upon death:
* The Kemurikage were women from the Fire Islands who died under extreme grief and sadness for having their children taken away. They transcended as dark spirits to haunt the warlords who kidnapped their children.
* The Painted Lady had a close connection to nature. After she died, she watched over the Jang Hui River.
* Fang, Avatar Roku's spirit guide, continued to exist within the Spirit World after he and Roku perished.
* Yue sacrificed herself by using the energy of Tui inside her to resurrect the Moon Spirit after it was killed. In the aftermath, she transcended as the new Moon Spirit, jointly with Tui.Escape from the Spirit World online game.
* Iroh developed a close connection to spirits during his life and, when he felt there was nothing more he could accomplish in the mortal realm, decided to venture into the Spirit World.
The following humans are known to have entered the Spirit World through different means but are stuck in their spirit forms:
* At least forty souls are imprisoned in the Fog of Lost Souls.
* Hundun was forced to meditate into the Spirit World seeking immortality after the Avatar of his era injured him in a fight. After countless ages of searching, he eventually discovered a technique that would restore what he lost and returned to the physical world when Avatar Korra opened the spirit portals to exact his revenge on the Avatar.
* Zhao was punished by La to be imprisoned in the Fog of Lost Souls for leading the siege of the Northern Water Tribe and killing Tui. Over the years, Zhao was driven into insanity due to his obsession of defeating Avatar Aang.
* Aiwei initially intended to enter the Spirit World to secretly converse with Zaheer following the attempted kidnapping of Avatar Korra. A misunderstanding led Zaheer to grabbing Aiwei and imprisoning him in the Fog of Lost Souls for eternity.
=== Spirits and mortals merging ===
It is possible for mortals and spirits to fuse beyond regular possession, which only leaves a mortal with spirit characteristics and potentially kills them afterward. The most famous case of a full merger is the Avatar, resulting from the union of Wan and Raava.
According to Father Glowworm, a spirit can absorb a human, granting the latter a form of immortality at the cost of their personality. On the other side, Yun demonstrated that the reverse was also possible, as he literally consumed Father Glowworm, thereby gaining several of his abilities and seemingly ending the spirit's independent existence. Yun speculated that Father Glowworm had been destroyed, dissipated, or remained alive within him as a result of their merger. In contrast, when a human and a spirit join together willingly, both maintain their personalities and separate identities. This was demonstrated by Wan and Raava as well as Unalaq and Vaatu.
Notably, the fusion of spirit and human does not grant immortality to the latter. All known Avatars were mortal, and both Unalaq as well as Yun were killed. However, in case of the merger between Wan and Raava their connection endured beyond death and led to a reincarnation cycle. As spirits cannot truly die and thus have to endure in some form beyond their human partner's demise, it is not known whether the reincarnation cycle is unique to the Avatar or also occurs for other human-spirit mergers. Unalaq believed that his fusion with Vaatu would result in a similarly functioning "Dark Avatar" which was supposed to exist for thousands of years. However, the Dark Avatar was never allowed to attempt reincarnation, as Vaatu was absorbed by Raava during Unalaq's death.
The following humans were possessed or merged with spirits:
* Yao (possessed by a spirit)
* Hunter (briefly possessed by the aye-aye spirit)
* Wan (merged with Raava during Harmonic Convergence, beginning the first Avatar Cycle)
* Governor's son (briefly possessed by a dragon bird spirit)
* Yun (merged with Father Glowworm)
* Unalaq (merged with Vaatu during the Harmonic Convergence of 171 AG, briefly creating the Dark Avatar)
* Korra (re-merged with Raava after she was extracted and destroyed by the Dark Avatar, starting the Avatar Cycle anew)
* Tokuga (briefly possessed by the dragon eel spirit)
== Trivia ==
* Bryan Konietzko stated that the radish lotus spirit might have once been a monkey that transcended after being blown through one of the spirit portals, its new appearance reflecting a turnip it had previously eaten.
* When he consumed Father Glowworm, Yun thought that him eating a spirit was "sacrilegious" and deeply damaged the spiritual balance as well as order.
== References ==
Category:A to Z
Category:Spirit World