- Lulu: "The fayth are people who gave their lives to battle Sin. Yevon took their souls, willingly given from their still-living bodies."
- Tidus: "Huh?"
- Lulu: "Now they live forever, trapped in statues. But when a summoner beckons, the souls of the fayth emerge once again. That's what we call an aeon."
- —Lulu explains fayth to Tidus.
The fayth (祈り子, Inorigo?, lit. "Child of Prayer") are humans who willingly had their souls sealed in statues in a state of dreaming in Final Fantasy X. Their powers allow a summoner to coalesce the power of pyreflies to create physical forms called aeons or other magical phenomena. In the world of Spira the fayth are the souls of the people who willingly underwent a ritual that removed their souls from their still-living bodies and sealed into stone tablets. This technique of creating fayth is known only by those from Zanarkand.
After Zanarkand's defeat at the hands of Bevelle, Yu Yevon, the ruler of Zanarkand, was at a loss. His summoners defeated, the Bevelle army was marching up the slopes of Mt. Gagazet towards the city of Zanarkand. Yevon converted those of his people still alive into fayth and placed them on a wall on Mt. Gagazet and then used these new fayth to summon a dream world modeled after Zanarkand. With the power of the fayth's dream, he summoned all of the buildings and all of the people who had lived there. This dream Zanarkand was meant to "preserve" Zanarkand for all time. After this Yu Yevon summoned an armor around itself and created Sin.
Yevon's daughter, Lady Yunalesca, and her husband, Lord Zaon, went to Bevelle with a means to stop Sin. Yunalesca, through means which are never explained, made Zaon into a powerful aeon, known as the "Final Aeon", for the first Final Summoning. Although she and Zaon defeated Sin, Yunalesca died, while the spirit of Yu Yevon possessed Zaon's aeon body, turning it into a new Sin.
The fayth's aeon forms are the physical embodiment of the fayth itself. For example, Anima's fayth is Seymour's mother. She felt immense pain during her life, and thus, Anima was created. Aeons usually embody the fayth's strongest emotion; in Anima's case, pain, and sorrow.
Despite her death, Yunalesca remained in the world of the living at the ruins of Zanarkand as an unsent. From there, she awaits the summoner who makes it to her abode to create an aeon from the summoner's guardian to fight Sin with. This allows the fayth within to finally rest as Yevon jumps to the body of the Final Aeon, creating a new Sin, and goes into a recuperative state; this time during which Sin is absent is called "the Calm". To ensure the summoner's readiness, they embark in a pilgrimage to visit the Yevon Temples around Spira to pray for their fayth and acquire the power to summon them as aeons.
The fayth grew tired of their dreaming after a 1,000 years and request Tidus, a product of their dream, to destroy Yu Yevon so they can rest at last. After Yu Yevon's defeat the fayth are freed to enter the Farplane, but as a result, Tidus and his world disappear as there were no longer anyone to summon them.
In Final Fantasy X-2 it is revealed that the fayth, who had sacrificed themselves to help Yuna defeat Yu Yevon, had become enslaved by Shuyin's darkness. Yuna and her friends manage to free the fayth from his influence by defeating him. During her journey to the Farplane Yuna meets Bahamut's fayth who tells Yuna about Shuyin and how the fayth tried to stop him but were unable to.
Each fayth has two physical forms (not counting the aeon form): The spirit-like fayth, and its soul form, sealed in a stone tablet.
- Zaon: The fayth of the first Final Aeon. Though he is only referenced in Final Fantasy X, he reappears in the depths of Via Infinito in Final Fantasy X-2. Apparently, his aeon form became a fiend called Paragon.
- Fayth of Bahamut: A child-like fayth who watched Tidus grow up in Zanarkand. Stationed at Bevelle Temple, he is the one who brought Tidus and Yuna together so the fayth can end their dreaming. Two years later, when the Gullwings defeat Anima, the last aeon twisted by Shuyin, Bahamut's fayth appears to the girls to apologize on behalf of the other aeons for attacking them and explaining why they did so. In both games, Bahamut's fayth acts as a representative for all fayth; except for Seymour's mother, Jecht and Zaon, Bahamut's fayth is one of only two designs that is original and not a reused model for NPCs. A notable aspect of the design is that the halo behind the aeon's head is present on the hood of the fayth's clothing.
- Fayth of Valefor: A young girl who lived at Besaid.
- Fayth of Ifrit: A male Crusader who looks to be in his prime. He was stationed at Kilika Temple. His character model is repeatedly used throughout the game, as well as for the Final Fantasy X-2 NPC Yaibal.
- Fayth of Ixion: A man who seems to be dressed in clothes from the seas. He was stationed at the Djose Temple.
- Fayth of Shiva: She was apparently a Macalanian priestess prior to becoming the fayth for her temple.
- Fayth of Anima: Seymour's mother, a tortured soul who suffers because her son, Seymour, only became more and more hungry for power after receiving the power of Anima from her fayth. She was stationed at Baaj. Her fayth design is one of the only ones not to be used by another NPC.
- Fayth of Yojimbo: A bodyguard in life, he was stolen from a temple to hinder the summoners' path. He ended up in what came to be known as the Cavern of the Stolen Fayth. His only companion is a dog named Daigoro. His is also a reused model for Crusaders, and blitzball free agent player Kyou and the Final Fantasy X-2 NPC Beclem.
- Fayth of the Magus Sisters: The three sisters became the fayth of Remiem Temple, though it is rarely ever visited due to its out-of-the-way location.
- Jecht: Tidus's father, the fayth of Lord Braska's Final Aeon.
Several aeonic forms have different names (for example Grothia, the name for Isaaru's Ifrit), implying that they are identical in appearance but separate in nature from the other aeons of similar form.
Lady Yunalesca is the only one described by Final Fantasy X as having created the fayth after her father converted all Zanarkand residents into fayth 1,000 years ago. She created the fayth of the temples that every summoner party visits before reaching Zanarkand to aid them in preparation for using the Final Aeon to defeat Sin. The summoner's guardian willingly becomes the Final Aeon's fayth, who then becomes a vessel for Sin once Yu Yevon enters the Final Aeon, using its form to build a new Sin. After the new Sin is defeated, the fayth is free to enter the Farplane. The only exception would be Zaon, the very first Final Aeon, who resides at the last floor of Via Infinito underneath Bevelle.
The fayth predate the Zanarkand war, since Zanarkand was the long-time home of the summoners. Summoners summon aeons, which are themselves associated with individual fayth. The "Dream of the Fayth" is a different manifestation performed by the fayth created from the Zanarkand survivors who allowed Yu Yevon to make them into fayth. Therefore, since summoners existed long enough before the Bevelle-Zanarkand War to make Zanarkand their city, they must have possessed the knowledge to create fayth.
Without any evidence to the contrary, it is to be assumed the fayth are at least as old as the existence of summoning itself; another great unknown is what exactly it takes to become a fayth.
Finally, the fayth are essentially different from spirits as they are in a state of dreaming, tied to Spira because of Yu Yevon. Though they are allowed to finally depart for the Farplane their aeons could be used in Spira by Shuyin. Furthermore, Tidus was conscious enough on the Farplane to whistle at Yuna when she was there, so it is possible that Farplane dead merely have a different type of consciousness.
There seem to be different levels of fayth. Bahamut's fayth acts as a sort of 'emissary of the fayth' for Tidus in his dreams or in Dream Zanarkand, and on the other hand, there are the remaining ten fayth, only appearing in a temple's fayth chamber. The hundreds of fayth gathered in the fayth spring near Zanarkand are never communicated with.
"Fayth" is an obsolete spelling of the English word, "faith". It is strongly believed to be an intentional use, giving religious undertones to the fayth, who were referred to as "children of prayer" in the Japanese version of the game.