The era said to be called the "Eternal Calm" begins when Yuna and her guardians defeat Yu Yevon, leading to Sin's death and beginning a Calm that was thought to last forever. As Yu Yevon's death ends the continued summoning of Dream Zanarkand, the fayth depart to the Farplane. With Shiva gone, the temple above the thawing Lake Macalania sinks and the Macalania Woods begin to deteriorate.
After Yuna's Calm began, the tradition of performing sendings seems to have ended. Final Fantasy X-2 Ultimania Omega elaborates that pyreflies continued to appear in great numbers as the destruction of Sin had broken the cycle of sending the dead to the Farplane resulting in the sudden increase of fiends, as pyreflies are their lifeforce.
With Sin's death, many Spirans become able to see more of their world with less fear of being attacked. While the Al Bhed become accepted by mainstream culture and provide their innovations to a wider market, the Guado have become demonized for their association with Seymour Guado and flee to the dying Macalania Woods with the intent to die there. Tromell, having originally intended to perish for his role in Seymour's actions, has a change of heart upon hearing the resident musicians, and decides to bring them and his people back to Guadosalam. Tromell is named the Guado leader as he decides to bring peace between his people and the Ronso, now led by Yuna's former guardian Kimahri Ronso, who quells his people's grudge on the Guado.
The Order of Yevon, having long been the power in Spira, crumbles as the result of its leadership falling apart with a political vacuum created in Spira, having been exposed of its dark nature, especially in Bevelle. During the first year, a former Yevonite monk named Trema began the sphere hunting craze that swept Spira while establishing the New Yevon party that is currently led by Praetor Baralai. The New Yevon party finds opposition in the Youth League, a faction led by Nooj, on the grounds that New Yevon keep secrets like their predecessor. The Youth League seeks to hunt down ancient spheres to publicize Spira's true history, whereas New Yevon merely seeks to catalog them and withhold certain things, such as the existence of Vegnagun, for fear of rousing unrest. Unbeknown to the Youth League, however, their endeavor is in part fueled by Nooj being possessed by a malevolent spirit called Shuyin, who drives Nooj to discover Vegnagun's whereabouts.
A third group led by Gippal, the Machine Faction, is neutral and salvages machina for improvement of the world. They also seek to study them and learn how to improve on them, which was not often done during the era of Sin. The Machine Faction has many Al Bhed members, but are by no means a purely Al Bhed faction.
The peace of Yuna's Calm is temporarily threatened when tension between New Yevon party and the Youth League rises prior to their leaders disappearing into the Farplane after Baralai is possessed by Shuyin, who intents to use the ancient machina weapon Vegnagun to wipe out Spira out of his grief of not being able to save Lenne, his lover and former songstress and summoner. The Gullwings dismantle the weapon and enable both spirits to rest in peace. Soon after, Nooj, Baralai and Gippal return and hold a speech in Luca, apologizing for their roles in the their parties' shortcomings while announcing that the Calm will continue.
During the events of Final Fantasy X -Will-, the Spiran Council has been established with Baralai as its leader. Yuna has founded her own religious order, the Yevoners, who use some of the ideals she saw in Yevon without the anti-machina policy and conspiracies the religion used to manipulate Spira with. Due to the abnormalities in the Farplane, the dead are beckoned back to Spira and Yuna's Calm ends as Sin is among the returned.
Nagi (ナギ) from Eien no Nagisetsu (永遠のナギ節) came from the word nagi.Nagi (凪) is a Japanese word meaning the state of calm wind (wind speed 0 to 0.2 meters per second). In Japan, the nagi state is the safest time period for fishermen and mariners to take off from shore.
- Final Fantasy X-2 Ultimania Omega p085