Below are the list of Masters and their Servants. Be warned though, you may be spoiled.
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Master: Kiritsugu Emiya (Fate franchise)
He remains consistent with the original setting of Fate/Zero and serves as the Master of Saber.
Servant: Saber - Artoria Pendragon (Fate franchise)
Also consistent with the original setting of Fate/Zero, summoned in the Saber class.
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Master: Tokiomi Tohsaka (Fate franchise)
Maintains his role from the original series.
Servant: Archer – Gilgamesh (Fate franchise)
Retains his arrogant demeanor from the original series.
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Master: Sola-Ui Nuada-Re Sophia-Ri (Fate franchise)
Instead of her fiancé Keyneth, she assumes the role of Master for Lancer.
Servant: Lancer - Kyoko Sakura (Puella Magi Madoka☆Magica)
Motivated by a desire to save her friends from a Witch's curse, Kyoko Sakura joins the War.
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Master: Kirei Kotomine (Fate franchise)
Retains his position from the original setting.
Servant: Assassin - Kenshin Himura (Rurouni Kenshin)
Known as the legendary hitokiri of the Meiji Revolution, Kenshin Himura participates in the War to protect his loved ones.
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Master: Waver Velvet (Fate franchise)
Maintains his character from the original setting, with a different Rider as his Servant.
Servant: Rider - Lelouch vi Britannia (Code Geass)
Summoned prior to his confrontation with Schneizel, Lelouch vi Britannia wields his Geass as his trump card.
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Master: Ryuunosuke Uryuu (Fate franchise)
Perishes early due to an accident during Servant summoning.
Servant: Caster - Jōnouchi Katsuya/ Joey Wheeler (Yu-Gi-Oh!)
Summoned as the Caster, Joey Wheeler aims to save his friends' souls, displaying remarkable luck in utilizing cards to summon monsters and invoke traps.
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Master: Sakura Matou (Fate franchise)
Selected as the Master of the Berserker class Servant instead of Kariya.
Servant: Berserker - The Warrior of Light (Final Fantasy XIV)
Responding to Sakura's call for help, The Warrior of Light is summoned, clad in menacing armor and wielding various weapons. Though powerful, he is bound by the constraints of the Berserker class, limiting his communication to nods and shakes of the head.
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Minor Characters:
Irisveil von Einzbern: Kiritsugu's wife but a very, very, very minor character.
Maiya Hisau: Same as Irisveil, a very, very, very minor character.
Keyneth: OG Lancer's master, but he now only serves as Sola's assistant because he can't stop simping her.
Risei Kotomine: He will appear later but would be a lot useful.
Zouken Matou: Dead
Shirou Emiya: Random Kid
Random pedestrians: Just there to die