Assassin (アサシン, Asashin?) is one of the seven normal Servant classes summoned for the Holy Grail War; Servants of this class are skilled at operating covertly, stealthy, and silently. This class is one of the weaker classes at fighting; as its members possess low attributes due to not having glorious legends as heroes; so it instead specializes in killing Masters rather than Servants. It is an oddity compared to the more formal knight classes who believe in fair duels and chivalry in combat; they will attack using the most unfair and favorable conditions; and with these conditions, it is possible for an Assassin to match and defeat other Servants. Deprived of a Master, Servants of the Assassin class generally possess the ability to remain with the world for about forty hours, which is roughly equivalent to a proficiency of B- in Independent Action.
The Assassins' special class ability is ‘‘Presence Concealment”; which allows them to remain undetected when spying or preparing to ambush their targets. The use of this ability during battle is the lifeline of Assassin; the greatest skill of each legally summoned Assassin is expressed as their Noble Phantasm; which all share the name Zabaniya -- the name of the 19 spirits that assist the angel Maalik in guarding Hell in Islamic mythology.
The system of the Fuyuki Grail War required originally that the Servants of the Assassin class must be one of the nineteen individuals known as Hassan i Sabbah -- the pseudonym shared by the leaders of the Hashshashin, a medieval Islamic sect. The name of the sect is the etymological root of the word "assassin;" and the class name itself thus acts as the catalyst to summon the members of the organization. The requirement noted above was based in the rationale that those who might truly be described as perfect assassins would normally remain anonymous; and consequently fail to become Heroic Spirits. The wraiths (亡霊, bourei?, lit. dead spirits), the leaders of the Hashshashin -- Heroic Spirit Candidates (英霊候補, Eirei Kouho?) that might have been properly inducted to the Throne of Heroes if not for the loss of their original names -- are thus regarded as qualifying in substitute of truly anonymous killers. With the corruption of the Grail during the third War; the absoluteness of this rule was compromised along with the disallowance of evil Heroic Spirits. Due to being selected from a group of Wraiths; their abilities are low.
There does not seem to be any such rule in the Fate/Extra or in the Fate/Apocrypha version of the Holy Grail War; The Assassin in Fate/stay night , summoned by Caster, is an exception. He is an aberration in the system, as another Servant summoned him. Heracles has qualifications for all classes besides Caster; so it is unknown how he would fit into the role of Assassin.
- 1st & 2nd Fuyuki War: Hassan-i-Sabbah. Details are unknown for the Assassin class Servants summoned during the First and Second Wars except for the fact that they were of the nineteen Hassan-i-Sabbah.
- 3rd Fuyuki War: Hassan-i-Sabbah. The Assassin Class Servant summoned during the Third War, briefly shown in Fate/hollow ataraxia; is an unnamed Hassan-i-Sabbah that utilizes the Cyber Phantasy version of Zabaniya.
- 4th Fuyuki War (Fate/Zero): Hundred-Faced Hassan. The Assassin Class Servant summoned during the Fourth War in Fate/Zero is the The Hundred-Faced Hassan summoned by Kirei Kotomine. Unique among the Hassan-i-Sabbah, he had in life the ability to take upon completely different personalities. As a Servant, he can summon up to eighty different bodies with different personalities simultaneously.
- 5th Fuyuki War (Fate/stay night): Sasaki Kojirou. The Assassin Class Servant summoned during the Fifth War in Fate/stay night is Sasaki Kojiro; summoned by Caster; He is an irregular Servant in both his existence and his class placement, as another Servant summoned him. Caster killed the original master who would have summoned a proper Hassan-i-Sabbah; and summoned the Servant for herself instead. Without a proper contract with a human, he was bound to the gate of the Ryuudouji temple; and created as a nameless wraith who shared similarities with the legend of Kojiro. He has a weak version of Presence Concealment that is his own version rather than the class ability; and he appears listed as "Assassin?" in the Fate/complete material III Servant section. Heracles, summoned as Berserker; also has the qualifications for the Assassin class.
- 5th Fuyuki War (Fate/stay night: Heaven's Feel): Hassan-i-Sabbah. The Assassin Class Servant summoned during the Heaven's Feel route of Fate/stay night is True Assassin summoned by Zouken Matou. He is a true Hassan-i-Sabbah summoned by killing the irregular Assassin after the war has started.
- Moon Cell War (Fate/EXTRA): Li Shuwen. The Assassin Class Servant summoned during the Holy Grail War of the Moon Cell in Fate/Extra is Li Shuwen summoned by Julius B. Harway. He would have originally been Lancer with the form of an older man; but he appeared as Assassin due to his Master desiring a young and ferocious Li Shuwen out of compatibility with himself. Lu Bu, summoned as Berserker; also has the qualifications for the Assassin class. Incidentally, Li Shuwen is the only proper Heroic Spirit that has been summoned within the Assassin class in the officially published media of the Fate franchise.
- Fate/Apocrypha: The Assassin Class Servants summoned during the Holy Grail War of ‘‘Fate/Apocrypha are Jack the Ripper and Semiramis.
- Snowfield War (Fate/strange fake): Zealot. The Assassin Class Servant summoned during the Holy Grail War of Fate/strange fake; is the Zealot summoned by Jester Calture. She is a female member of the Hashshashin who excelled in the use of all of the techniques her organization developed; but was unable to succeed the seat of leadership due to her compatriots' fear of her, as well as being unable to create a technique of her own.
- ↑ Jonnobi - マスターを失っても40時間ほどは現世にとどまれる。
- ↑ Jonnobi - アサシンというクラスそのものがアサシン召還の触媒となる。
- ↑ Jonnobi - ハサン・サッバーハ（亡霊・英霊候補）: 冬木の聖杯戦争において必ずアサシンのクラスをまとって召還される亡霊（英霊候補）の郡体。 正体はアサシンの語源となった暗殺教団（イスラム教イスマイル派）の歴代頭首たち。英霊でないのは決して名を残さなかったため。
- ↑ Fate/side material - Assassin class encyclopedia entry - "Since they are selected from a group of Wraiths (Heroic Spirit Candidates). Originally under the name "Assassin,” their abilities are low.” (もとから“アサシン"という名称で群をなす亡霊 (英霊候補)なので、能力そのものは低い。)
- ↑ Japanese Type Moon Wiki: 筋力Ｄ 耐久Ｄ 敏捷Ｂ 魔力Ｅ 幸運Ｂ
- ↑ Japanese Type Moon Wiki - アサシン (EXTRA): Fateシリーズに登場するアサシンでは唯一の正式な「英霊」である。