Saber's True Name is Altera Larva (アルテラ･ラーヴァ, Arutera Rāva?, localized as Young Altera), or Attila (アッティラ, Attira?), but she is different from the Altera of Earth. She is the reborn form of Attilaight cell, no longer connected to the Velber.
Saber is born at the end of the game after the defeat of Sefar.
Altera appears in Fate/EXTELLA LINK as playable DLC character.
In the beginning of the story, Altera is happily walking around Mare Aurum with Hakuno Kishinami. She decides they should return home before Nero Claudius and Tamamo-no-Mae get upset at them for being out too long. On their way back though, Altera suddenly stops when they come upon a newly area generated. Attack Programs then appear before her and Hakuno to their surprise. The pair run away since Altera isn't yet matured to fight. They're able evade the programs for little bit before they're completely surrounded. Suddenly, Charlemagne appears and saves them from the Attack Programs. After he defeats the remaining programs, Altera suddenly stares at the sky. Hearing something calling to her, she apologizes to Hakuno and leaves.
She later arrives in Carolus Patricius where she meets Scáthach, and requests an audience with Karl der Große. Upon meeting him she recognizes his voice as the same one that called to her earlier. She asks him why he is invading SE.RA.PH., to which he answers it is to make his wish come true. She then asks he'll still wish for it even he hurts other people. Karl answers none will understand his wish, though his wish is for all of them. After he talks about his wish at lengthening, Altera describes it as wrong, though she knows no one can stop Karl from assimilating everything with the power of the Oracle.
If Hakuno's forces manage to undo Astolfo's Oraclization, Altera asks Karl if he's sad about losing Astolfo. He replies he has dedicated his body to peace, God, and the World; claiming to be unchanging and universal. Altera tells him it's sad be alone, to which Karl responds he doesn't know sorrow, only knowing the fear of God and the World.
If Hakuno's forces retake Mare Aurum and undo Elizabeth Báthory's Oraclization, Altera comments on her arrogant yet honest personality that follow their dreams.
If Hakuno's forces between Karl's forces at Mare Origio, Scáthach is sent out to bolster his forces. Before departing though, she tells Altera she will return soon with presents.
After Karl is defeated, Altera is reunited with Hakuno, Nero, and Tamamo. She later returns to Mare Aurum where she is lectured at by both Nero and Tamamo for leaving without permission. When asked about her experience with Karl, she only says that it made her sad. She is last seen partaking in a celebration party with Hakuno's other Servants.
If Hakuno's forces personally prevent Gilles de Rais from recruiting Artoria Pendragon into the New Holy Empire, Altera tells Karl they'll need another third Spirit Core to complete the World. She ask Karl if he truly wants for them to join with the World to replace the third one when he suggests it. Referring to her as his elder sister, Karl answers they'll save the World with only two if there are only two.
After Karl stares at the Monolith, Altera asks him if he truly wants to destroy all bad civilizations and bring eternal peace. He answers he will bring salvation to all, including her, and bring forth the will of God and the World.
Returning to her adult form, Altera regrets she may have placed her burden on Karl when he touched the Monolith in his previous life since both her and it are connected to Velber. She realizes though Karl doesn't consider it a burden when he says he dedicated his entire life to the purpose he foresaw. She then realizes Karl intends to use the Monolith to assimilate SE.RA.PH. and Oraclize everyone at once. When Karl states this plan of action will only assimilate 60% of SE.RA.PH. while the rest will fade away, Altera realizes he'll still continue even at the cost of his humanity.
Later, back in her child form, she confronts Hakuno's forces in Mare Mellum. Expressing her intention to protect Karl, she returns to her adult form. She tells the others that Karl decided to destroy the present in order to gain the future. She continues she doesn't want to judge or deny, as she knows he is both right and wrong. After she is defeated, Altera returns to her child form, and collapses from the strain.
Altera is taken to Charles Patricius, and put to sleep by Nero and Tamamo. After Karl is defeated, she has recovered, and participates in the celebration party with Hakuno's Servants.
When Karl senses Charlemagne is coming, Altera asks him what he'll wish for once Charlemagne is gone. He answers his wish will always be to give universal peace to all, and believes God and the World desire for him to bring his wish to SE.RA.PH. Altera however questions if Karl's wish is truly desired.
Recognizing her true identity of Sefar, Gilles tries to kill Altera to prevent Moon Cell's destruction at her hand. Karna defends her as citizen of SE.RA.PH. despite her true identity since she's no longer serves Velber. After Gilles leaves, Karna apologizes to Altera for the former's attempt on her life. She then asks him to bring a message to Hakuno. Her message is later brought to Hakuno by Archimedes, who was asked by Karna to deliver it. In the message Altera says she is waiting in Mare Luxuria, and she needs to tell something important about Hakuno and Charlemagne.
When Hakuno's forces arrive in Mare Luxuria, Altera greets Hakuno and Charlemagne. She thanks Nero and Tamamo for their concern for her. She then expresses her intention to protect Karl, as he is alone in the world like she is. She apologizes to Hakuno for wanting to protect Karl, and thanks them for their understanding. Changing into the adult form, Altera says she feels great affection for both Karl and Charlemagne. She then prepares to fight for Karl, as she considers him family and shares his goal of creating a worthy civilization. An Oraclized Karna and Arjuna then appear alongside Altera; Karna understands her determination to stand by Karl. She reveals Karl touched the remains of Sefar in his lifetime and foresaw his destiny to pacify Europe. Even though they're not related by blood, she still considers Karl family as she understands his pain. She wonders if her choice is wrong, but stands by it since she cannot abandon Karl who chose life over destruction. She apologizes to Hakuno for choice, but Karna tells her that her apology is unnecessary, as he believes it is noble to fight for the affection of one instead of welfare of the many. Thanking Karna and Arjuna for decision to fight with her, Altera goes to fight Hakuno's Servants.
After being defeated, she reverts back to her child form, and collapses from the exhaustion of the battle. She is brought back to Charles Patricius where she is put to sleep by Nero and Tamamo. She later wakes up in her adult form, wanting to go with Hakuno and others to fight Karl. Thanking Nero for her concern, she says if Karl's tragedy began when he touched Sefar's remains, then it's responsibility to see this battle through. Charlemagne apologizes to her for putting her in this situation, but Altera says it's fine since it's her destiny as his and Karl's elder sister.
Altera and Hakuno's other Servants assault Carolus Patricius where they fight against facsimiles of Gilgamesh, Iskandar, and Artoria created by Gilles led by an oraclized Jeanne d'Arc. She and Arjuna use their Noble Phantasms to destroy the Karl Cannons Jeanne has ordered to fire upon their allies. After defeating the facsimiles of the Top Servants and Gilles, Hakuno's Servants defeat Jeanne. After Jeanne and Gilles disappear, Altera realizes that being oraclized helped Jeanne see Karl's wish for world peace.
With the assault on Carolus Patricius successful, Altera nearly collapses from mana exhaustion due to her Spirit Core still being in mid-repair. Karna points out she shouldn't have been fighting, as even the simplest tasks put a greater strain on her than his and the others' Noble Phantasms at full power. Tamamo explains Altera's actions show how much she cares about Karl, but Altera says she also wants to protect Charlemagne. Due to her poor condition, Altera stays behind with Karna and Arjuna while Hakuno, Charlemagne, Nero, and Tamamo go to fight Karl. She is eventually recovers enough to witness Karl's final moments, and bids him farewell when he disappears. She then escapes Carolus Patricius with Hakuno, Nero, and Tamamo when it begins to collapse with Charlemagne's disappearance.
Later in Mare Aurum, Altera, back in child form, sits with Hakuno as they reminisce about Charlemagne. She tells them that Charlemagne told her that he won't be summoned again since the Moon Cell recorded him and Karl as the same person. She reveals though that Hakuno can use the Regalia to summon new versions of Karl and Charlemagne from their memories. She explains they will be Attack Programs at first, but with enough battle records the Moon Cell save records of them. Changing to her adult form, Altera tells Hakuno they'll need to create their own battles for this purpose. She however knows there is a higher chance they may only record the battle data of mere Attack Programs. She also knows recreating two complete Servants is a greater task than Moon Cell creating NPCs with robust AI and abundant data. She continues she and Hakuno will use Karl's wish for world peace and Charlemagne's role as a chivalrous knight to serve as a basis for their new respective records. She hopes that Moon Cell will eventually record Karl and Charlemagne as separate people, given that they are powerful Servants. She continues SE.RA.PH. will need many Servants as possible for the day when Velber returns. She and Hakuno then begin the long and arduous task of recreating Karl and Charlemagne.
Before learning how to fight in her child form, Saber transformed into her adult form temporarily in order to battle.