True Assassin (Fate/stay night)

Assassin (アサシン), designated as True Assassin (真アサシン) in reference materials, is the Assassin-class Servant of Zouken Matou in the Heaven's Feel route of Fate/stay night's Fifth Holy Grail War. He is designated as True Assassin because he is the proper Heroic Spirit meant to be summoned under the Assassin class rather than the aberration in the War, Sasaki Kojiro, summoned as an irregular Assassin by Caster.

Identity
True Assassin's identity is, the Persian "Old Man of the Mountain" who lead an assassination organization originating in the Middle East. While he was a legendary leader who became the origin of the word Assassin, there were nineteen different people who took up the position of Hassan-i-Sabah over many years. There is a new one born each time someone takes up the position, and True Assassin is one of those nineteen. As with the others, his true name and face before becoming an assassin and a Hassan is still lost.

Hassan-i-Sabah has appeared in many stories, known as the leader of unidentified assassins. All those who became the leader imitated his name and appearance, and there was no other way of succession permitted. The history behind the establishment of the organization is long and complicated, and they followed through on strict and frantic doctrines. While other sections of the religion were willing to use violence in accordance With their teachings, they were the only extreme group that preached of "obedience to absolute power."

Hassan lead from an occupied castle in the mountains, turning it into a base for founding the religious organization. After becoming an organization, they used "assassination" as their political measure. Hassan's methods were extreme, so they used drugs to enhance their mental state and accomplished tasks exceeding human capabilities. The origin of their name, Assassin, comes from a nickname given to the secret killers using the hashish. Their works were precise and unparalleled, and their name was known even in different countries. They never showed themselves as the hid in the mountains, and they killed those who opposed their God. Their way of being became a perfect subject for European poets.

While Hassan's story was dramatized, he still became a legend, and after some time, "Assassin" acquired a new meaning as "secret killer." Their existence was exaggerated as time passed, and they have now established themselves as an illusion that is not inferior to that of legendary heroes in the least. The "assassination agency" that still exists in modern times is part of the cogwheel that Hassan established, and the Old Man of the Mountain continues to exist within the sect no matter how many years pass since its formation.

Appearance
His appearance is that of a slender, dark man with his right arm bandaged. His right arm is described by Saber as useless flat board, incapable of doing much. His face, revealed by Sakura in the Heaven's Feel scenario, is that of a skull, without any skin. This inspires Sakura to say that he tries to live for eternity when he already lost his identity.

Fate/stay night
The Assassin-class Servant originally summoned for the Fifth Holy Grail War is Assassin. He is an aberration summoned by another Servant, Caster, so he is not one of the Hassan. True Assassin is only summoned during the Heaven's Feel route after Zouken Matou decides to participate within the Holy Grail War.

Heaven's Feel
Zouken Matou disgusted as he witnessed Rider lose to Saber, and enraged at Shinji's incompetence as a Master. He decides to participate in the Fifth Holy Grail War by using Assassin's flesh as a catalyst for summoning True Assassin.

True Assassin emerges from the flesh of Assassin and later attacks Lancer.

Abilities
Assassin is a proper Assassin-class Servant, so he is not suited to direct combat like Kojirou. He cannot match other Servants in direct combat, and he specializes in killing Masters instead of their Servants. His proper role is to lurk in the shadows and strike at the right opportunity. He is quickly beaten back by Lancer, Rider, Saber, and Archer when forced directly into close combat, and readily admits that he has no chance against them under normal circumstances, opting to utilize the Shadow against Saber and Lancer.

He is an anti-hero, and he is not a proper Heroic Spirit due to all of the Hassans being classified as Wraiths. He is inclined towards evil, so he is more resistant to All the World's Evil than regular Heroic Spirits. While he is close in nature to it, he will still have his energy drained should he touch it. He has the Self-Modification skill, allowing him to attach and fuse a totally different body to himself. The rank reflects how far he is from being a proper hero. He is able to last around a day without a Master before he will run out of energy and fade away.

He is unafraid of abilities like Invisible Air's Strike Air despite not having enough prana to counter it due to his Protection from Wind. Invoked with the chant "Allah Akbar", it is a curse passed down in the Middle East that is used to ward off storms. It is a prayer that invokes Allah in order to ward off the Wind God Jinn. It allows him to charge at a wind attack that would instantly shred him apart while screaming in delight, instantly nullifying it. Curses to ward off storms were a necessity for travels in the desert, making it the only magecraft used by him.

He has proper Presence Concealment unlike Kojirou, allowing him to remain perfectly hidden even to the senses of Servants. Erasing his presence, it is suitable for spying because it is nearly impossible to find him. The rank of the ability drops substantially after he begins to attack.

Summoning
Assassin's summoning is unique compared to that of other Servants due to being brought forth after all seven Servants have been summoned. Through an unknown process, Zouken takes the defeated Kojirou and turns his body into the flesh of Assassin. It begins with Kojirou's chest bursting open from Assassin's "deformed, spider-like arm" emerging from it. Still alive, Kojirou begins to feel his internal organs becoming those of someone else before finally expiring. Assassin then fully enters the world in a form much like an insect that devours the rest of Kojirou's body, slowly becoming more like a man and acquiring human wisdom for his empty brain.

He is fully formed after drinking every last bit of blood, but he is still somewhat undeveloped, shown his inability to speak human language. He can originally only make chirping sounds like an insect, but later is able to speak while displaying a strained speech pattern. He needs more experience in order to be fully functional, so he devours Lancer's heart to add to his own intelligence. Afterward, he is able to speak fully and rationally without showing any of the previous insect-like qualities. Saber notes that his voice is strong and clear in contrast to his appearance, and that it is similar to that of Lancer.

Dirks
Assassin's employs numerous Dirks (ダーク), small black daggers meant to be utilized as throwing weapons rather than as melee weapons. Their tips are hooked, making removal from the target a hard task once they have struck. He has over forty of them, and he can run out in battle because they are finite in number. Due to his attachment to them, he carefully picks them up after each battle. He is very accurate, can throw multiple Dirks like bullets without any visible movement, and always aims for vital points. They are not extremely potent weapons, as while they would be fatal if they were to hit, abilities like Protection from Arrows and Saber's ability to read the path of projectiles make them easy to manage and no different from thrown stones.

His precision with the weapons is close to that of Archer, allowing him to throw accurately while constantly moving. He launches them during the small openings between the swings of the opponent's weapon, and they are thrown so that the opponent will not be able to see them if circumstances allow. He utilizes his agility to jump from various positions including walls and ceilings, all while hurling numerous Dirks from each location. This creates an unavoidable rain of daggers from all directions that cannot be blocked or avoided.

"Dirk" was originally the name of a type of thrusting dagger traditionally used in Scotland, imprinted with Celtic designs and patterns, and they were utilized as actual weapons until around the eighteenth century. They were relegated to ceremonial uses after that, but the British Empire adopted it as a weapon in the armed force and navy after incorporating Scotland into their empire. Calling the weapons "Darks" would be incorrect, though such a thing would never happen.

Combat Tactics
Assassin does not fight opponents at close range due to being no match for other Servants, instead using his Dirks at mid-range while constantly moving away from his opponent. He retreats while maintaining a proper distance between them, moving with a beast-like pace rivaling Lancer while he retreats that allows him to slither across the ground without having to slow down around obstacles. He is able to jump extremely well, and his movements are compared to a spider, snake, and scorpion. Lancer notes that after he is injured, he is unimpeded by it. He thinks rather than healing that Assassin has employed drugs to keep the wound from affecting him.

He employs a constant battle strategy used against Heroic Spirits and even regular humans should he fight them. While he throws numerous Dirks in battle, the act is not done in order to kill the opponent. While each strike is indeed intended to be fatal, their real worth is to gauge the opponent's strength. The first Dirk measures their mobility, and the second measures their action principles. He remains seven meters away at all times, keeping a distance at which only projectile weapons are useful and still remain able to measure the opponent's skill. If he is unable to kill them in one blow, he will force them to a place where it is possible.

He drives the opponent into a corner by cutting their limbs and tiring their bodies, all in preparation for his fatal attack, his Noble Phantasm, Zabaniya: Delusional Heartbeat. Even if they are in preparation, they are still meant to kill, so he notes that Kirei Kotomine's ability to last against them as long as he does is admirable. The daggers are merely to analyze the target's skill, create the perfect opportunity, and then smash their heart with his arm. Once he knows their capabilities and is assured that they are tired and wounded, he measures out a fatal strike to be blocked so that he has time to utilize Zabaniya.

The ritual is a chore for him that brings him no joy, but it can also be a weakness if the ritual is known to the enemy. He sticks to it methodically, so seeing it through Lancer's eyes allows Kirei to form a countermeasure and temporarily defeat Assassin. Zabaniya creates a copy of the opponents heart for Assassin to crush, but it has no effect on Kirei's blackened heart.