Assassin (Fate/stay night)

Summary
Assassin is the Assassin-class Servant of Caster, an irregularity that shouldn't exist under the Assassin class, yet summoned through Caster's machinations. His true name is ostensibly Kojirou Sasaki, a legendary Japanese swordsman, theorized to have the true name of Tsuda. However, Sasaki Kojirou never existed; instead, the Servant summoned is a nameless samurai who dedicated his entire life to the mastery of swordsmanship, his sheer skill becoming a legend on the level of a Noble Phantasm on its own. His life resembles the legend of Sasaki Kojirou, and so he is summoned under his name and with his legend.

He appears in Fate/Grand Order as both his original summoning as an Assassin and as a Nameless Saber who duels Musashi Miyamoto in The Tournament of the Seven Blade-Master Heroic Spirits.

Powers and Stats
Tier: High 7-A

Name: Assassin, "Sasaki Kojirou", "Tsuda", the Nameless Samurai

Origin: Fate/stay night

Age: Unknown

Gender: Male

Classification: Assassin-class Servant

Powers and Abilities: Superhuman Physical Characteristics, Enhanced Senses (He has exceptional eyesight, superior to Archer, allowing him to discern the dimensions of Excalibur through Invisible Air), Master Swordsman(His swordsmanship is so refined that it has reached the level of a Mystery beyond human possibility, allowing him to launch three perfectly simultaneous slashes from three different directions), Precognition, can conceal his presence, his style is not something that can be read or acclimated to, Supernatural Luck, Minor Fate Manipulation (Servants with B-rank Luck or higher can change their own fates to evade inevitable outcomes such as having their hearts destroyed by Gáe Bolg), Soul Manipulation (All Servants can feed on souls to replenish their mana), Intangibility and Invisibility in spirit form, Immunity to Conventional Weapons (Servants cannot be harmed by weapons of the modern era like firearms or bombs if they are not enhanced by a supernatural component or infused with magical energy), Resistance to Mind Manipulation, Regeneration (Low-Mid over time; can regenerate from a serious wound that blasted open his chest and exposed his ribs)

Attack Potency: Large Mountain Level (Can fight Saber, Archer, and Lancer, would've killed Saber with Tsubame Gaeshi if it landed, and can just barely redirect blows from Berserker).

Speed: Massively Hypersonic (Saber struggled to keep up with him, with every one of her blows being parried by his attacks. Intercepted Archer and proceeded to trade blows with him after)

Lifting Strength: Unknown

Striking Strength: At least Large Mountain Class

Durability: At least Large Mountain Level

Stamina: High. Due to his irregular nature, he can survive for twenty days without a Master, and even if he had his heart destroyed, he'd be able to continue fighting for a brief period of time.

Range: Extended melee range.

Standard Equipment: Intelligence: Assassin is a peerless swordsman, having reached a realm transcending the realm of men through nothing but hard work and single-minded dedication. He is stated to have the greatest swordsmanship amongst all of the Servants in the war, far surpassing Berserker, who is more than qualified for the Saber class, and Saber, who is renowned in life for being one of Britain's finest knights. Even the The King of Heroes is no match for him in a contest of swordsmanship. Furthermore he can clash evenly with his chief rival, Musashi Miyamoto, who had also reached the pinnacle of swordsmanship and could collapse all possibilities into a single outcome, with their respective skills being stated to transcend time and space itself. As such, his skill as a swordsman is stated to have reached the state of true emptiness, reaching the unreachable existence of Infinity. Personality wise he is also serene and calculating, rarely losing his composure and allowing him to easily perceive even the slightest weaknesses in the target with his keen eyesight, even outmatching the similarly perceptive Archer in close combat.
 * Monohoshi Zao: Assassin's extremely long blade, measuring at 150cm. Its size would make it unwieldy and nearly impossible to use efficiently for nearly any wielder, but Assassin wields it masterfully, as his swordsmanship has long surpassed the bounds of human possibility.

Weaknesses: The Monohoshi Zao, while a finely crafted weapon, is still mundane. This means that it will chip or bend if forced to clash directly against something not made by men, like Saber's Excalibur. Tsubame Gaeshi can only be performed properly if performed on level ground and will become imperfect if the Monohoshi Zao is bent or chipped in combat, leaving gaps through which a swift enough opponent can dodge. Assassin is not particularly interested in finishing his opponents due to his transient existence and is more than likely to attempt to prolong a proper sword fight in order to enjoy it.

Notable Attacks / Techniques:

Class Skills
Presence Concealment: The capacity to hide one's presence as a Servant. It is a common skill to the Assassin class. Suitable for spying, though low enough that other Servants would easily detect him if he was nearby. He does not have it by virtue of being an Assassin, but it is an intrinsic ability of his as a martial artist that allows him to cut himself off from the world.

Personal Skills
Eye of the Mind (False): Assassin has the natural ability to avoid danger based on an innate sixth sense refined through combat experience, so much so that it borders on precognition. Assassin's rank is A, meaning that it is so refined that the effects of visual obstructions are reduced, allowing him to gauge the exact length and width of Excalibur despite being rendered invisible by Invisible Air. He is said to have the best eyesight amongst the Servants summoned for the Fifth Holy Grail War.

Knowledge of Respect and Harmony: Assassin's techniques cannot be properly perceived by his opponents no matter how many times they're demonstrated, as a result it is impossible for an opponent to get used to them. Thus the tenth, hundredth, or even thousandth encounter against him will feel the same as the first, so his techniques will always retain their effectiveness against his opponents.

Vitrification: Due to Assassin's serene state of mind, he is immune to mental interference. In addition, his B+ Rank in this skill allows him to conceal his presence if he pleases, allowing him to simulate the True Assassin's Presence Concealment skill to a limited extent, making it difficult for even Servants to detect along with his lack of mana and a true Noble Phantasm.