Amnesia (term)

Amnesia is a recurring plot device in the Final Fantasy series. The type of amnesia usually depicted is retrograde amnesia, where the afflicted loses their past memories but is able to function normally and retain new memories. Other than this however, the cause of the memory loss varies, but universally is used to conceal some secret about a character's past integral to the plot. How they recover their memories also varies.

Final Fantasy III
In the 3D versions, Luneth, Arc, Refia and Ingus have forgotten they were born on the surface world and were brought to the floating continent and given to foster parents by Cid Haze. Desch lost his memories while being in suspended animation for a 1000 years. He doesn't regain his memory until the party reaches the Tower of Owen.

Final Fantasy IV
While sailing to Baron, Leviathan attacks the party's ship and Yang is washed overboard, awakening on the Baron shorelines without his memories and being appointed a captain of the guard due to his Monk training. When Cecil arrives in town Yang and his men attack him, and Cecil and his allies defeat Yang in battle, the blows restoring his memory.

Final Fantasy V
Galuf suffers a blow to the head prior to meeting Lenna and Bartz, and loses all his memories save for his name. He recovers a bit of his memories but does not remember in full until his granddaughter Krile appears, the sight of her restoring his memory. Due to his injury Galuf feigns head trauma and swoons as a running gag when he acts questionably.

Final Fantasy VI
Terra begins with no memories save for her name and a few brief recollections of the Gestahlian Empire, due to the Slave Crown used to control her mind distorting her thoughts. Once the magicite Maduin is brought to her, Terra's mind clears and she recovers her memories.

Gau's father has repressed the memories of Gau's birth, convincing himself he never had a wife or son in real life, and believes that in a dream he was married and lost his wife giving birth to a "demon child" he abandoned on the Veldt.

Another character that suffered from amnesia is Rachel. She went to Mt. Kolts with Locke before she fell off a collapsing bridge, causing her to lose her memories.

Final Fantasy VII
Cloud suffers from a complex series of memory disorders. After impressing Zack and Tifa's memories of him combined with his own ideal image of himself as a SOLDIER, much of Cloud's memories distort into a false reality where he joined SOLDIER and became Sephiroth's partner, forgetting Zack even existed. Cloud's memory remains full of inconsistencies and holes that he is unable to explain, and further toll on his identity is aggravated by Mako poisoning upon him being washed into the Lifestream. It is only after Tifa journeys into Cloud's Subconscious that the two of them can reconstruct Cloud's true memories and restore his mind.

Chocobo Sage is an old sage who knows the secrets of breeding the best chocobo, but his memory is poor and is not able to remember more than one clue at a time.

Final Fantasy VIII
Prolonged use of Guardian Forces results in memory loss due to the GF's presence in the controller's brain residing in the same areas that govern long-term memory. The party's loss of memory isn't revealed until Irvine tells Squall, Quistis, Zell and Selphie that the five of them, along with Seifer and Ellone, were orphaned and raised by Edea Kramer at a seaside orphanage.

As the five were sent to Gardens to train as SeeDs, they began to use GFs and forgot about their childhoods, Irvine remembering due to not using GFs until he met up with the party as he has never trained as a SeeD.

Garden Faculty is aware of the deleterious effect of the GF, but urge students to ignore any GF criticism they may hear from other forces. Quistis at first refuses to believe that Headmaster Cid Kramer would allow such a dangerous thing, but is forced to acknowledge the truth of the matter.

Final Fantasy IX
Both Zidane and Garnet have no memories of their early childhoods. Zidane was abandoned on Gaia by Kuja at an early stage of life, and remembers nothing of Terra save for a blue light. Garnet was born in Madain Sari as "Sarah", and she and her mother fled to the Mist Continent by boat when the village was destroyed. Sarah's mother perished before arrival, and the King of Alexandria found Sarah and took her as his own child to replace his recently deceased biological daughter, named Garnet. The Final Fantasy IX Ultimania elaborates that the girl had lost her memories in the calamity, and didn't question it when her new adoptive parents let her know she had always lived in Alexandria Castle.

Sir Fratley was Freya Crescent's lover in Burmecia who left to travel the world and never returned. Freya set out to find her lost love, but when she does, she discovers Fratley is suffering from amnesia and does not remember her. It is implied they become a couple again after Kuja's threat has been removed, although Fratley never regains his memory.

Final Fantasy X
In the world of Spira, people may suffer from "Sin's toxin" if they go too close to Sin. Tidus plays along with it and initially fakes amnesia to make up for his lack of knowledge of Spiran culture.

There is a man who actually got Sin's toxin after the destruction of Kilika. He can't remember anything including his own name so he just sits at the port, hoping someone will recognize him.

Final Fantasy XIII
During the War of Transgression, 600 years ago, Fang and Vanille were tasked to become Ragnarok and lay waste to Cocoon. Fang ended up becoming Ragnarok alone and her incomplete Ragnarok cracked Cocoon's shell, whereupon the two were placed in crystal stasis by Goddess Etro.

600 years later, Fang and Vanille recover from crystal stasis, but Fang has lost all memories of her previous Focus and her time as Ragnarok. Vanille, wanting to protect Fang, hides the truth. Although Fang never truly recovers her lost memories, she can piece together the true events from the suspicious way Vanille is acting.

Final Fantasy XIII-2
As a time traveler from 700 years in the future, Noel Kreiss possesses knowledge of the events between Serah Farron's time and his. However, his memory is affected by the paradoxes and corruption of the timeline, and he is unable to recall some basic historical facts which would help direct him and Serah on their journey. The effect gets worse as the timeline keeps changing due to their actions.

Mog, Serah and Noel's companion on their quest, also lost most of his memories when he fell into a paradox in the Ocean of Time. By solving the anomalies in Oerba of 300 AF and 400 AF, Serah and Noel can help Mog remember his past.

Due to her existence as a paradox effect, Alyssa Zaidelle's memory is corrupted, although the events of the true timeline regarding her manifest during her dreams.

Final Fantasy XIV
Cid nan Garlond suffered amnesia in the aftermath of the Calamity, and was taken in by Father Iliud of the Church of Saint Adama Landama. As "Marques", he worked as a priest until Alphinaud sought him and the adventurer out to revive the Scions. Cid slowly recovers his memories as they scour Coerthas for his missing airship, the Enterprise, and only once it is fully repaired and he is piloting it, does he fully recall his past.

Bravely Default
Ringabel has amnesia, to the extent that he has forgotten his real name and adopted a moniker supposedly given by the townspeople of Caldisla. He carries a mysterious journal and uses the author's written accounts to justify the party's next objective. After defeating Alternis Dim aboard the Grandship, the dark knight's helm breaks to reveal his face is that of Ringabel's. Ringabel takes to comparing the journal Alternis dropped with his own, realizing the written accounts are similar. After defeating Alternis a second time Ringabel starts to recall fragments of his memory, and after awakening three crystals in the third version of Luxendarc, he finally remembers his past as the dark knight, along with hailing from a different Luxendarc than his companions, and that Airy is deceiving the party.

Airy claims to have amnesia every time the party passes through the Holy Pillar only to awaken in a world where the Great Chasm is still present. This is only a ruse to convince the party to reawaken the crystals in each world they appear in, as they still retain their memories when they pass through the light.

Dissidia Final Fantasy and Dissidia 012 Final Fantasy
Warriors summoned to World B to fight arrive with no memories. As they fight, their memories of their past lives and worlds gradually return, but if they are defeated in battle, Shinryu absorbs their memories of the cycle they were fighting in and revives them in the next cycle.

The warriors retain the memories of their home world, but have no recollection of previous cycles. Those who are not defeated retain their memories into the next cycle, but once defeated, all memories of previous cycles are absorbed.

The Warrior of Light and the other warriors of Cosmos believe he is suffering from a more severe case of amnesia, but it's later explained he has no memories of a life outside the cycles because he was born during the cycles.

After Onion Knight saves Terra from the Cloud of Darkness, she has no recollection of her forced battle against the Onion Knight due to her powers going out of control, something Onion Knight attempts to hide from her for her protection. As soon as she learns from Kefka Palazzo about the event, Terra becomes disturbed and nearly relapses until Cloud Strife puts her back to her senses at her request.

Trivia

 * The incarnation of amnesia related instances in school centered settings in Final Fantasy is likely a parallel to the occurrence of the coming of maturity and adulthood in relation to one's memories over their lifetime, as it is believed that as one ages and engages in the responsibilities of adulthood, memories of nostalgic and cherished importance are phased out and are harder to remember.