Cycle (term)

In Dissidia Final Fantasy and Dissidia 012 Final Fantasy, Cycles are the name used to describe the recurring wars that are fought between Cosmos, the goddess of Harmony, and Chaos, the god of Discord. Unbeknownst to the two factions, the wars are actually masterminded by Shinryu and Cid of the Lufaine, so that each time a faction wins the survivors are killed and everyone is revived to begin a new war again. The purpose of this repetition of cycle is for Shinryu to study the world, although how and why is unclear. There has been twenty cycles seen or alluded to in total in the two games.

1st to 11th cycles
Cosmos lost all these cycles.

12th cycle
This is the main story of the eponymous Dissidia 012 Final Fantasy. In this cycle, many new Cosmos warriors are introduced. All of the new Warriors of Cosmos are killed by Manikins, which is why Shinryu is unable to revive them in the next cycle.

13th cycle
This is the main story of the first Dissidia Final Fantasy, as well as the bonus chapter of Dissidia 012 Final Fantasy. In this cycle, several Chaos and Cosmos Warriors have switched sides while Cid feels guilty and has rebelled against Shinryu. At the end of this war, the Cosmos side wins and the heroes apparently return to their respective worlds by Cid possessing Chaos to teleport them away.

14th to 18th cycles
Because of Cid's actions, the pact with Shinryu was broken and the dragon sought vengence of being robbed of the power, experiences and memories of the summoned warriors. To that end, Shinryu forged a pact with Chaos, restarting the cycle of conflict. However, Cosmos's warriors achieve victory over the opposing side since. By the 18th cycle, Chaos is driven mad by his defeat to the point of personally decimating both the Warriors of Cosmos, and his own. Feral Chaos, the berserk form of Chaos, was then sealed away by Cid. However, a manikin of Feral Chaos runs rampant.

19th cycle
During this cycle, Shinryu has accumulated enough knowledge and strength from the wars and evolved into his final form, called Shinryu Verus. Little else is known about this cycle.

20th cycle
At the 20th Cycle, Chaos went to slay Cosmos herself, but Cid managed to save Cosmos' power, and sealed her in the Cavern of the Earth near Melmond. At this point, Chaos had nothing else to do, so he went against his own creators, and challenged Shinryu. Cid then sealed the northern continent away to make sure that Shinryu and Chaos could not touch him or Cosmos. Cosmos herself lost the power to summon soldiers, which is why she ended up being kept safe in the Cavern of the Earth. It is implied that the Confessions of the Creator is the aftermath of the 20th cycle, and that there is nothing left but the moogles and the Manikins. It is also implied that the five characters that the player chooses are summoned through Cid this time around to stop Chaos once and for all.

Final Fantasy X
In Spira, spiral of death takes place due to Sin: his never-ending revival and bringing death each time he is summoned. Eventually the spiral was broke bringing time called Eternal Calm.