According to Final Fantasy X Scenario Ultimania Sin's body is composed of pyreflies and in that respect, it is no different from a common fiend. However, Sin draws in pyreflies to replenish its strength whenever damaged, and thus conventional attacks cannot defeat it. According to the Final Fantasy X Ultimania Omega, its body is formed as a result of gravity magic used to draw in further pyreflies from the atmosphere, and compressing them densely. Sin can recover the separated parts of its own body, known as "Sinspawn," because Sin can repair its body more efficiently by taking in pyreflies that have already been condensed, rather than freshly absorbing pyreflies that drift around the surrounding areas.[1]

Sin's destructive capabilities are tremendous, as it can control gravitational forces and thus fly. People who touch Sin are sometimes carried, unharmed, to remote places. This is because Sin's body is supple and can suck up those who touched it and then expel them. People who have gotten close to Sin may get muddled up and experience hallucinations. This is called "being affected by Sin's toxin," but the true reason is that the high density of pyreflies that form Sin's body have an adverse affect on the low-density amounts of pyreflies present within the bodies of those who approach it.

Sin is immune to most conventional forms of weaponry and is highly resistant to attack, able to project a barrier to protect itself. Spirans believe that only the Final Aeon can kill Sin, and all attacks the party wages on Sin in Final Fantasy X only serve to wound it. Sin's signature attack is a huge blast of energy from its mouth known as "Giga-Graviton," an attack so powerful it can induce tectonic plate movements visible from outer space. Its other body parts are capable of using lesser Gravity-based attacks. Sin has an affinity for water, and can often be encountered lurking in such an environment. It can blend into, absorb and use the water it inhabits as a weapon.

Whether Sin's abilities change depending on which Final Aeon forms its core is unknown. It is implied the post-Braska's-Calm Sin never reached its full strength, as the Final Aeon at its core still exerted some influence over it, slowly being taken over by Yu Yevon.

Sin was created during the Machina War between Bevelle and Zanarkand a thousand years ago. Bevelle relied on machina for weapons and Zanarkand used summoners. When Zanarkand was losing, Yu Yevon, a summoner of Zanarkand and its leader, devised a plan to both defeat Bevelle and preserve the city of Zanarkand forever. Yu Yevon called the surviving people of the city together and transformed them into fayth as conduits for a massive summoning that created a spectral version of Zanarkand from the dreams of the former Zanarkand inhabitants.

Yu Yevon set this dream Zanarkand out to sea, then called pyreflies to himself to craft the first Sin. This was the only Sin that never had an aeon at its core. Sin was given three objectives: to protect the summoning of dream Zanarkand, to ensure it was not discovered, and to destroy any city that grew too large or relied too heavily on technology. The strain of trying to control Sin was beyond Yu Yevon, and the process destroyed his mind, removing any conscious control he may have had over it. Sin thus became a monster guided by its instincts, and indiscriminately attacked the machina civilizations all over Spira, starting with the true Zanarkand itself. Yu Yevon was reduced to a husk who existed only to summon.

To allow Spira a reprieve and hope for salvation, Yu Yevon's daughter, Yunalesca, presented a way to destroy Sin: the Final Aeon, a powerful aeon born from a bond of love. Sacrificing her husband Zaon for the ritual, he became the Final Aeon and destroyed Sin, but the Final Summoning killed Yunalesca. Yu Yevon's spirit possessed Zaon's body, and over time transformed into a new Sin with Yunalesca's Final Aeon at its core. During this time, the new Sin was too weak to terrorize Spira, establishing a temporary period of Calm.

Apparently the only one able to create the Final Aeon, Yunalesca became an unsent and remained in the Zanarkand Dome to create a new Final Aeon for summoners who complete their pilgrimage. As told in the official timeline in Final Fantasy X Ultimania Omega, during the First Calm, the survivors began reconstructing Spira, focusing on Bevelle. After Yu Yevon had regenerated Sin, Spira's plight began anew. The second incarnation of Sin destroyed the remaining machina civilizations and thus machina use began to fall out of favor.

The Yevon temple was established in Bevelle, which began the tradition of paying homage to Yevon and Yunalesca; these teachings, as well as the prohibition of machina, were subsequently adopted by the world at large. Seizing on public sentiment, the temples took control of Spira. The new religion established Sin as a punishment for people's sins, promulgating the story that the Calm would arrive with the Final Summoning. The temples shifted the blame for Sin's return onto the people of Spira, and maintained stability by instilling in them the hope that through atonement, Sin will eventually be banished permanently. In truth, Yunalesca and the upper echelons of the Yevon temples know Sin will always return, but their teachings give Spira hope and keep its citizens from succumbing to despair.

Some six hundred years later, a summoner named Gandof defeated Sin, tearing the Calm Lands asunder and isolating the Remiem Temple, thus creating the Second Calm and becoming the first high summoner. Gandof suffered the same fate as Yunalesca had and died. This gave credence to Yevon's teachings, and doubts about the temples subsided. As before, the Calm was short-lived, and Yu Yevon rebuilt Sin, which started its rampage as the third Sin appeared with Gandof's Final Aeon as its core.

Gandof was posthumously titled "high summoner," a title which would from then on be bestowed on all who defeated Sin. Statues of him were placed in Yevon's temples and his story was told to all Spirans as an example of honor and sacrifice to be followed. To defeat Sin, summoners would journey through a series of temples, gathering powerful aeons at each one in preparation for obtaining the Final Aeon in Zanarkand and combating Sin.

For hundreds of years, this cycle continued—summoners would go on a pilgrimage to hone their abilities as they traveled to the ruins of Zanarkand and met Yunalesca, who would transform one of their guardians into a new Final Aeon. The summoner would give his or her life to destroy Sin with the Final Summoning, and Yu Yevon's spirit would possess the Final Aeon and turn it into a new Sin.

As Sin attacks large settlements, Spiran towns rarely grow beyond a certain size. The biggest city in Spira is Bevelle, followed by Luca, but countermeasures are taken so that those cities aren't attacked by Sin by having the Crusaders attract Sin's attention and avert its course.

Braska, Jecht and Auron are the most recent band of summoner and guardians to defeat Sin. They made their way to Yunalesca and Braska obtained the Final Aeon. Though Braska held onto the hope that this time, Sin would not return, Auron believed otherwise. Jecht, originally a citizen of dream Zanarkand who had accidentally ended up in Spira, became Braska's Final Aeon. Before this, he tasked Auron with finding a way to the dream Zanarkand and taking care of his son, Tidus. The Final Summoning killed Braska and Jecht became the new Sin.

Ten years later, Jecht, still aware within Sin, although only barely, brings Sin to dream Zanarkand, and he and Auron take Tidus into the world of Spira. As Tidus travels with Braska's daughter Yuna as her guardian, Auron accompanies them and teaches Tidus about Jecht and Braska. Tidus is made aware of Jecht's spirit resting within Sin, and is told Jecht wants Tidus to kill him to free him from his fate of terrorizing the world. They run into Sin many times and witness the destruction it brings forth.

When the party confronts Yunalesca, she tells them the Final Aeon would not destroy Sin permanently, but Braska chose this path to give the people of Spira hope. Yuna disagrees, saying her father believed he could free Spira. Denouncing the tradition as false hope, Yuna refuses to sacrifice one of her guardians. Yuna and her guardians destroy Yunalesca, and with her, the way to create a new Final Aeon.

Now made aware of Yu Yevon's existence, Tidus suggests a new way to destroy Yu Yevon's spirit within Sin. The party wages a full scale attack on Sin with the airship, Fahrenheit, and enters its mouth. In the deepest part of Sin, they find a recreation of the dream Zanarkand in ruins, where Jecht awaits them. The party destroys Jecht in his Final Aeon form and Yu Yevon emerges.

Yuna calls her aeons one by one and Yu Yevon possesses them, and the party destroys them as well. With no aeons left to control, Yu Yevon becomes vulnerable and is killed. Yuna performs a sending to place his spirit at rest. With Yu Yevon's defeat, Sin explodes, and the Eternal Calm begins.



The Farplane has become unstable to the point that beckoning outside of it manifests the dead in Spira. Sin returns, ending the Eternal Calm, and Yuna theorizes it was the result of someone beckoning it. She delivers a speech to a crowd of people announcing she will defeat it once more.