- This article is about the actual concept of heart in the mythology of Fabula Nova Crystallis: Final Fantasy. For the concept of soul, which was united with the concept of heart in the English localization in the Lightning Saga series, see: Soul (Fabula Nova Crystallis).
People's hearts are pure chaos. Formless and ever-changing—a mystery no one can solve. That is why humans are such contradictions. One moment they're at each other's throats, the next they're forming shaky alliances.
Hearts (心, Kokoro?), also incorrectly localized as souls and spirits, are an integral part of the Fabula Nova Crystallis: Final Fantasy subseries. It is a more "specified" concept of a soul: whereas soul is the "essence of humanity", heart is the "essence of a person", giving a person their individuality. Gifted to humanity by the Goddess Etro, they act as a balancing force in the universe. Hearts are the means through which humans have the strength to challenge both the fal'Cie and the deities.
In the localized versions of the Final Fantasy XIII games, the distinction between "heart" and "soul" is blurred. In the English localization of Final Fantasy XIII-2, the term "spirit" is incorrectly used instead of "heart". In the localization of Lightning Returns: Final Fantasy XIII, the term "soul" is used for the concepts of both "heart" and "soul", and interchangeably with "heart". This has caused some confusion for players.
Valhalla is the realm where human souls once returned before being reborn anew. The wise god Lindzei used the blood that had spilled from Etro to create man's body; his soul was fashioned from the Chaos. These wisps of Chaos filled the vessels that Lindzei had made and thus humanity was born. When a person died, his soul returned to the Chaos in Valhalla, the unseen realm where the goddess Etro rules.
When humans were created by Lindzei from Etro's blood after her suicide, they were without a heart. After her death Etro moved on to Valhalla, and was entrusted with keeping the balance between the visible realm (the world of the living) and the unseen realm (the world of the dead) by the creator goddess Mwynn, who was soon consumed by a substance known as chaos.
Etro felt an affinity with humanity who are bound to follow her in death. As the humans pass on to the unseen realm, Etro gifts them with pieces of chaos, making them a key factor in sustaining the balance of the universe. The heart acts as a "warehouse" for the soul. When a human dies, their heart dies, mostly likely passing to the unseen realm where they rest forever. This state of holding chaos within physical bodies makes humans unique, as they are drawn to both the visible and unseen realms, while other beings are tied only to one world.
As stated in Final Fantasy XIII-2, people with abundant chaos in their hearts are sensitive to things others miss: they can hear the words of the seeress, and thus the prophecies. As stated in Lightning Returns: Final Fantasy XIII, the deity Bhunivelze, and likely his creations Pulse and Lindzei, cannot see hearts because of their links to chaos. Bhunivelze despises it, seeing chaos and the hearts residing within it as a polluting force. Despite this, he can manipulate a person's heart if they become unbalanced. The fal'Cie, and by extension the deities that created them, are said to have a type of physical heart that mimics emotions, but these are not true hearts.
When in the Augusta Tower 200 AF, Noel explains the difference between humans and duplicates to Serah. He says the the goddess gave humanity "hearts". When Lightning enters crystal stasis after her final battle with Caius, she takes Serah's heart and soul with her.
After Etro's death Chaos floods the visible realm. Without a deity who would continue to give hearts to the souls to the now freed Chaos, the cycle of reincarnation is broken. As mankind can no longer reproduce, humanity is rendered biologically immortal.
After Lightning awoke from her crystal stasis, Bhunivelze removed Serah's soul from Lightning. Along with it, a part of Lightning's heart was also removed due to her having locked her heart away after her parents' death. Lightning's heart became connected with Serah's soul during her sleep, and Serah's soul merged with the lost part of Lightning's heart, manifesting as Lumina.
The main goal of the Order of Salvation is easing the burden on the hearts of the remaining population, since the memories of the souls of the dead are troubling them. According to the Order this is the wish of Bhunivelze. This may originate from Bhunivelze's inability to see human hearts. Lightning meets a projection of the advocate for the souls of the dead, Cid Raines, who informs her about "bonds" which allow a person to use the limitless power of Chaos, but doing so requires a contact of a living person with the soul of a dead one.
On the final day, when Bhunivelze appears in the Luxerion Cathedral, he uses Hope's body as his "avatar". Before his battle with Lightning, he reveals to her he used Hope as a means of studying human hearts. The god begins to show emotions supposedly unknown for fal'Cie, leading Lightning to realize Bhunivelze accidentally absorbed Hope's heart, and decides to use it to save humanity. The fake Serah Bhunivelze had created to keep Lightning acquiescent admits to Lightning she lacks Serah's heart. During the final battle, Lightning uses the bonds she made with Nova Chrysalia's people, and her link with the Chaos via Serah's soul, to unite humanity into a "sword" to strike down Bhunivelze.
Kokoro (心?) means "heart, mind, mentality, emotions, feelings" in Japanese.
- In the Datalog of the English release of Final Fantasy XIII-2, "heart" is incorrectly localized as "soul" despite the word "soul" not appearing in a single entry in the Japanese release.
- In Final Fantasy Type-0, the substance phantoma is described as "souls", though it exhibits traits synonymous with both hearts and souls.