Before Final Fantasy XIV
Long ago, Cait Sith was a familiar of the Mhachi High Voidmage Cessair, who foresaw the flood of Sixth Umbral Calamity due to disruption on the land's aether caused by Mhach's destructive campaign against Nym and Amdapor in the War of the Magi. Her people attempted to evade the calamity by creating the Void Ark with a thousand sealed voidsent powering it, only for it to end in disaster as not even Cessair can control the voidsent's leader Scathach. Eventually, Cessair and 53 other void mages had to sacrifice themselves to keep Scathach and the other voidsent sealed away with Cait Sith the only survivor. He was tasked to ensure the Void Ark would not be disturbed as it drifted in the Sea of Clouds for centuries.
In the aftermath of the Seventh Umbral Era, the calamity caused by Bahamut undid the seal that bound the voidsent Diabolos in the Lost City of Amdapor. Though defeated by the Warrior of Light, Diabolos escapes and makes his way to the Void Ark where he regains his strength while removing the seals on his fellow voidsent. When the Warrior of Light is hired by the sky pirate Leofard of the Redbills to search the Void Ark for treasure, Cait Sith makes his presence known when Diabolos retrieves the Queen's Coffin that contains Scathach and takes it through a voidgate. He tells his story while imploring the sky pirates help him track down the Queen's Coffin before Scathach is released.
Like many of the Warrior of Light's other allies from across the world, Cait Sith and the Redbills delivered supplies to Sharlayan to aid in the construction of the the Ragnarok, a ship capable of space travel.
Cat sìth (pronounced "Caught Shee") is a fairy creature from Celtic mythology, said to resemble a large black cat with a white spot on its breast. Legend has it that the spectral cat haunts the Scottish Highlands. It literally translates to "mound cat", referencing the fairy forts commonly held to house fairies of all kinds. English speakers may be familiar with its usage in the term bean sí, banshee.The
Some common folklore suggested that the Cat Sìth was not a fairy, but a witch who could transform into a cat and back up to nine times. After the ninth transformation, they would be unable to return to human form. This is speculated to be the origin of the proverb "a cat has nine lives", as opposed to some other number.