Fate/zero takes place 10 years prior to the events of Fate/stay night, detailing the events of the 4th Holy Grail War in Fuyuki City. The War of the Holy Grail is a contest in which seven magi summon seven Heroic Spirits to compete to obtain the power of the "Holy Grail," which grants a miracle. After three inconclusive wars for the elusive Holy Grail, the Fourth War commences.
Founded by the Einzbern, Matō, and Tōsaka families centuries ago, the Einzbern family is determined to achieve success after three successive failures, no matter the cost. As a result, they have elected to bring the hated magus killer, Kiritsugu Emiya, into their ranks, despite his methods and reputation as a skilled mercenary and a hitman who employs whatever he can use to accomplish his goals. Though Kiritsugu had once wanted to become a hero who could save everyone, he has long since abandoned this ideal upon realizing that saving one person comes at the cost of another's life. For the sake of humanity, he will ruthlessly destroy anything and anyone who threatens the peace of others.
However, Kiritsugu finds himself deeply torn between the love he has found for his new family - his wife Irisviel and their daughter Illya - and what he must do to obtain the Holy Grail. Meanwhile, Kiritsugu's greatest opponent appears in the form of Kirei Kotomine, a priest who cannot find any sense of fulfillment in his life and sets his sights on Kiritsugu as the possible answer to the emptiness he feels.
- Kiritsugu Emiya (衛宮 切嗣 Emiya Kiritsugu )
- Voiced by: Rikiya Koyama
- Master of Saber, adopts a strategy of exploiting a magus' weak point using technology. A coldblooded assassin skilled in hunting magicians. Entered the Einzbern family to realize his lifelong wish: to save the world using the power of the Holy Grail. Has Irisviel appear in Fuyuki City as Saber's master in order to allow him to move more freely.
- Kirei Kotomine (言峰 綺礼 Kotomine Kirei )
- Voiced by: Joji Nakata
- Master of Assassin, works for Tokiomi and does everything he is asked to do to the best of his ability, but lacks fulfillment, which he sees mirrored in Kiritsugu, for whom he feels a compulsive hatred. After Assassin dies, he becomes the Master of Archer who kills Tokiomi Tosaka.
- Irisviel von Einzbern (アイリスフィール・フォン・アインツベルン Airisufīru fon Aintsuberun )
- Voiced by: Sayaka Ohara
- Heroine of the story, the mother of Illyasviel von Einzbern and Kiritsugu's wife. A homunculus prototype created by the Einzbern family with the idea to give birth to an ultimate homunculus. Like many of the Einzberns, she is skilled in alchemy. Irisviel serves as Saber's proxy Master, since Kiritsugu believes that he and Saber are incompatible.
- Tokiomi Tōsaka (遠坂 時臣 Tōsaka Tokiomi )
- Voiced by: Sho Hayami
- Father of Rin Tōsaka and Sakura Matō, Master of Archer, arrogant and manipulative, arranges for Kirei Kotomine to be his "pupil". Thinks highly of Kotomine and has him serve him.
- Aoi Tōsaka (遠坂 葵 Tōsaka Aoi )
- Voiced by: Hasumi Ito
- Mother of Rin Tōsaka and Sakura Matō. Childhood friend of Kariya Matō. Though she is devastated by Tokiomi's decision to adopt away Sakura, she quietly accepts the decision as the wife of a mage.
- Waver Velvet (ウェイバー・ベルベット Ueiba Berubetto )
- Voiced by: Daisuke Namikawa
- Master of Rider, future Lord El-Melloi II. Steals his teacher's artifact and uses it to summon Rider. Plans to use the Grail to force the Magus Association to recognize his genius. Despite his difficulties with Rider's overbearing nature, Waver and his Servant form a strong relationship.
- Maiya Hisau (久宇 舞弥 Hisau Maiya )
- Voiced by: Ayumi Tsunematsu
- Assistant to Kiritsugu Emiya. She is cold and professional, which makes it easier for Kiritsugu to act as he needs to. Armed with a Steyr AUG.
- Kariya Matō (間桐 雁夜 Matō Kariya )
- Voiced by: Tarusuke Shingaki
- Uncle of Shinji Matō, Master of Berserker, makes a deal with Zōken Matō that he will win the Grail War in exchange for Sakura Tōsaka's freedom. He is the only member of Matō family who truly loves Sakura, and is upset that Tokiomi allowed his younger daughter to be adopted by Zōken. However, the war is taxing on Kariya, not only because of his lack of formal training, but also due to the nature of the Matō family's magecraft and the demands required to maintain Berserker.
- Ryūnosuke Uryū (雨生 龍之介 Uryū Ryūnosuke )
- Voiced by: Akira Ishida
- Master of Caster, sociopathic serial killer who summons Caster after murdering a family and using their blood as a component in the summoning ritual. He does not seek the Holy Grail, but follows Caster in order to find new thrilling ways to kill people and relieve his boredom.
- Kayneth El-Melloi Archibald (ケイネス・エルメロイ・アーチボルト Keinesu Erumeroi Achiboruto )
- Voiced by: Takumi Yamazaki
- Master of Lancer, a nobleman from the Magus Association and genius magus. His artifact is stolen by Waver Velvet, but he manages to summon Lancer anyway. While he holds the command spells for Lancer, the energy to materialize the Servant is maintained by Sola-Ui. He is confident in his abilities and takes pride in his heritage, but finds the extent of Kiritsugu's untraditional and underhanded tactics both offensive and unexpectedly challenging to overcome.
- Risei Kotomine (言峰 璃正 Kotomine Risei )
- Voiced by: Masashi Hirose
- Kirei Kotomine's 80 year old father, a priest in the Church, the regulator of the 4th Holy Grail War. He is a friend of Tokiomi Tōsaka and actively supports him. While he is proud of his son, who has demonstrated himself to be a perfect heir, Risei fails to understand Kirei in any sense.
- Sola-Ui Nuaba-Re Sophia-Ri (ソラウ・ヌァザレ・ソフィアリ Sorau Nuazare Sofiari )
- Voiced by: Megumi Toyoguchi
- The daughter of the head of the spiritual evocation division. She is engaged to Kayneth as a result of a strategic marriage arrangement and the decision of her family to entrust their crest to her brother instead. However, she is coldhearted and does not reciprocate Kayneth's love for her; instead, she becomes infatuated with Lancer, who in turn does not reciprocate her feelings and regards her only as his Master's wife.
Servants participating in the Fourth Holy Grail War and their true identities:
- Saber (セイバー Seibā ) - Arturia Pendragon (アルトリア Arutoria )
- Voiced by: Ayako Kawasumi
- The same character from Fate/stay night. Known as the King of Knights, also known as King Arthur who obtained the magical "Sword in the Stone", she maintains a high code of honour. Emiya was quite tempered to find out that the legendary King Arthur is a girl. Though she and Kiritsugu are Servant and Master seeking the same ultimate goal of peace, their differing ideological perspectives result in a strained relationship where Kiritsugu does not directly acknowledge Saber. Her Noble Phantasms are Excalibur - The Sword of Promised Victory (約束された勝利の剣（エクスカリバー）Ekusukaribā ), Invisible Air - Bounded Field of the Wind King (風王結界（インビジブル・エア） Inbijiburu Ea ), and Avalon - The Everdistant Utopia (全て遠き理想郷（アヴァロン） Avaron ).
- Archer (アーチャー Āchā ) - Gilgamesh (ギルガメッシュ Girugamesshu )
- Voiced by: Tomokazu Seki
- A rogue servant in Fate/stay night, the King of Heroes. He dislikes the presence of Saber and Rider in particular since they were kings like he was. Much to Tokiomi's displeasure, Gilgamesh has difficulty acting covertly or regaining his temper when his considerable pride is wounded. His Noble Phantasms are Gate of Babylon - The King's Treasure (王の財宝（ゲート・オブ・バビロン） Gēto Obu Babiron ) and Enuma Elish - The Star of Creation that Split Heaven and Earth (天地乖離す開闢の星（エヌマエリシュ） Enuma Erishu ).
- Lancer (ランサー Ransā ) - Diarmuid Ua Duibhne (ディルムッド・オディナ Diarumuddo Odina )
- Voiced by: Hikaru Midorikawa
- A Servant with two Noble Phantasms: Gae Buidhe - The Golden Rose of Mortality (必滅の黄薔薇（ゲイ・ボウ） Gei Bō ) and Gae Dearg - The Crimson Rose of Exorcism (破魔の紅薔薇（ゲイ・ジャルグ） Gei Jarugu ), which can counter Saber and Berserker's abilities. As a knight, he holds a strong sense of honour in battle and loyalty to his master. Despite being enemies, he and Saber share a mutual respect for one another.
- Rider (ライダー Raidā ) - Iskander (イスカンダル Isukandaru )
- Voiced by: Akio Ohtsuka
- The King of Conquerors, who desires to defeat Saber in particular because he believes her ideal regarding kingship are deluded and that she would thrive as one of his followers. Derives his status as Rider from a set of divine bulls and chariot purportedly a gift from Zeus, known as Gordius Wheel - Wheel of Heaven's Authority (神威の車輪（ゴルディアス・ホイール） Gorudiasu Hoīru ), summoned when Iskander slices the air with his sword. His two known Noble Phantasms are Via Expugnatio - Distant Trampling Domination (遥かなる蹂躙制覇（ヴィア・エクスプグナティオ） Via Ekusupugunatio ), the trampling attack used by the Gordius Wheel and Ionioi Hetairoi - Army of the King (王の軍勢（アイオニオン・ヘタイロイ） Aionion Hetairoi ). His eccentric and overbearing personality along with his incredible abilities creates difficulties for his Master and their opponents.
- Caster (キャスター Kyasutā ) - Gilles de Rais (ジル・ド・レェ Jiru Do Rē ),
- Voiced by: Satoshi Tsuruoka
- Commonly known as Bluebeard. A Servant who derives pleasure from first providing his victims a moment of relief before terrorizing them and then killing them. Expresses an interest in Saber because he has mistaken her for Jeanne d'Arc, with whom Bluebeard has an infatuation. His Noble Phantasm is Prelati's Spellbook - Text of the Sunken Spiraled City (螺湮城教本（プレラーティーズ・スペルブック） Purerātiīzu Superubuku ).
- Berserker (バーサーカー Bāsākā ) - Lancelot of the Lake (サー・ランスロット Sā Ransurotto )
- Voiced by: Ryotaro Okiayu
- Previously known as the Black Knight. A Servant who possesses the ability to use practically any object as a Noble Phantasm, allowing him to match Gilgamesh in combat. His madness has reduced him to a mindless, though dangerously skilled, fighter. Despite his insanity, he is still able to instinctively recognize Saber. His Noble Phantasms are For Someone's Glory - Not For One's Own Glory (己が栄光の為でなく（フォー・サムワンズ・グロウリー） Fō Samuwanzu Gurōrī ), Knight of Honor - A Knight Does Not Die with Empty Hands (騎士は徒手にて死せず（ナイト・オブ・オーナー）Naito Obu Ōnā ), and Arondight - The Unfading Light of the Lake (無毀なる湖光（アロンダイト） Arondaito ).
- Assassin (アサシン Asashin ) - Hassan-i Sabbah (ハサン・サッバーハ Hasan Sabbāha )
- Voiced by: Sachie Abe, Takuo Kawamura, Eiichiro Tokumoto
- Assassin is actually the reincarnation of the Assassin Order composed of several entities rather than just one. They act as reconnaissance agents for Tokiomi and Kirei after Gilgamesh "kills" one of them. They can only be truly defeated if all of them are killed. Their Noble Phantasm is Zabaniya - Delusional Illusion (妄想幻像（ザバーニーヤ） Zabānīya ).
The 2011 issue of Type-Moon Ace magazine reported that an anime adaption of Fate/zero was green-lit for production. It is produced by studio Ufotable and began airing in October 2011. This is the third anime production in the "Fate" series, following the 24 episodes "Stay Night" adaptation and the "Unlimited Blade Works" movie. Nico Nico Douga and Aniplex will simulcast "Fate/Zero" worldwide with eight different language subtitles (Korean, Chinese (Traditional & Simplified), English, French, German, Italian, and Spanish). Aniplex of America will sell the Fate/Zero Blu-ray Boxset, with English subtitles in North America through Rightstuf.com.
The anime was originally slated to run continuously 26 episodes, but was later given a season break between 13 and 14 to allow for better animation. The first season ran from October to December 2011 and the second season begins April 2012.