Invisible Air: Barrier of the Wind King (風王結界, Fū-Ō Kekkai?) is a sheath of wind that covers Excalibur and conceals it so that it cannot be easily recognized as the famous holy sword of King Arthur and expose her identity. It is a Bounded Field closer to magecraft than a Noble Phantasm that is made up of multiple layers of wind compressed into super-high pressure air with a massive amount of magical energy, which distorts the refraction of light and renders what is inside completely invisible. For the male King Arthur, Invisible Air acts as one of the seals along with the Restraints of the Round Table to Excalibur Proto's true power. While it has no basis in history, Kinoko Nasu figures it would be something Merlin could have managed because Heroic Spirits with overly famous Noble Phantasms generally have ways to hide their identities.
Upon Excalibur, it takes on the shape of the blade and renders it as an invisible sword that doesn't appear even as sparks fly off of it. It lacks the capacity to annihilate the enemy like Excalibur, being more suited as a "sharp tool" in battle. It isn't used for any particular strength, but it is easier to use in battle than Excalibur and it is a trump card that can bring about victory if used well. It is also possible to implement the barrier on something other than the sword. She can form the barrier in the area around her or as a quick defensive wall of wind, which she can keep active for a number of minutes with her magical energy. She uses it in Fate/hollow ataraxia to completely envelop the entire Central Building in an unbreakable protection. She releases it like an arrow to cover the body of her Yamaha V-Max motorcycle in Fate/Zero. Using the compression of the pneumatic umbrella surrounding her, she decreases the air resistance to zero to increase the vehicle's speed and keep the back wheel firmly against the cement with the pressure.
It is rather simple in execution, but it proves tremendously effective in hand-to-hand combat. The barrier isn't a vacuum, so the air constantly whirling around the blade is essentially a weapon. It increases the damage and cutting power of an attack, and the amount of magical energy released from each strike is high enough that it is visible to the eye. It also provides for an increased accuracy and defense against opponents unfamiliar with the nature of her weapon as it is difficult for the opponents to parry lunges and thrusts from Saber. They cannot discern the length, width, reach, or trajectory of the blade, or even the fact that it is even a blade until they actually make contact with the weapon, which leaves them constantly on guard due to having to rely solely on Saber's movement to decipher her attacks. They are confused both offensively and defensively, only allowing them to approximate the movements of the strikes and keep outside of her range to avoid being easily struck down. Against an opponent who can figure out the nature of the weapon quickly and correct the visual disturbance, such as Assassin with his Mind's Eye (Fake) ability, someone who is already familiar with the weapon, such as Berserker, or someone with a resistance to visual impediments, it becomes nothing more than wind around a sword.
Once the barrier is released so that Excalibur can be used, the previously compressed wind surges around her chaotically, creating a vacuum as it diffuses into the air with enough force to knock over normal people and shake heavy, firm trees like a typhoon. The compressed wind can also instead be released as a single use projectile weapon called Strike Air: Hammer of the Wind King (風王鉄槌, Fū-ō Tettsui?). Acting like a hammer made out of wind, it creates a gale made out of super high pressure condensed air that is powerful enough to easily crush and blow away armies and fling a stone slab weighing several tons into the air as if it were nothing. It is a long range attack with a constant amount of damage that is not influenced by Saber's physical condition or her level of magical energy. It can only be blocked by overwhelming it with a higher amount of magical energy. It can also be used to accelerate her own body towards her opponent, allowing her to travel at three times her normal speed. By holding the sword in a backward wide stance, she releases the air and changes into a supersonic bullet that charges towards her opponent. If working together with another person, the partner can use the vacuum left behind by the attack to immediately rush in behind it by using the surge of air taken in by the vacuum as a SlipstreamWP. After releasing it, she can recall it by compressing the surrounding air to reform the barrier.
When Artoria manifests as a Saber, this Noble Phantasm was something that conceals her sword, but when she manifests as a Lancer (including the Altered version), Invisible Air is treated as nothing more than a “Wind Noble Phantasm”. Used together with the Mana Burst Skill, it brings about the reinforcement of her Agility and a super-jump boost effect. Using all the stockpiled wind at once to fire a long range, area of effect attack (Strike Air) that mows down the enemies is still possible. Differing from Saber's version of Strike Air that is more of a piercing type, Lancer's version will mow people down. She primarily uses this Noble Phantasm to augment her attack power.
 Fate/complete material III: World Material - The Servants of the Fifth Holy Grail War: Saber, p.020-021 [T]
Master: Emiya Shirou
Alignment: Lawful Good
Armament: Armour, Sword
Noble Phantasm: C
Once up on a time, there was a king in England named Arthur Pendragon. He was the legendary king who staunchly defended the land from the invading Saxons for a long period of time.
The name Arthur, written in the fashion of Romans is “Artorius”. Its feminine form is “Artoria”, which is the true name of Saber.
Artoria was born between Uther Pendragon and a Queen hailed from the rival kingdom. She grew up under the guidance of the True Magician Merlin, and became the king after pulling out the Sword of Selection. Later, she led Lacenlot, Gawain, and other famed knights to achieve innumerable deeds. They engaged the King of Saxons at the Battle of Badon Hill and brought peace to the land of Britain. Because the Scabbard of the Holy Sword stopped her from aging, Artoria continued to reign as the ideal king. It was ironic that Queen Guinevere and the serving knights grew more distant from Artoria precisely because she was too ideal. In the civil war that raged at the end of her reign, she crossed blade with her very own son, Mordred. At that instant, she pledged her service as a Heroic Spirit after death in exchange for striking a pact with the World. The one wish she hoped the Holy Grail could realise was “redo the selection of the king”. In legend, the body of King Arthur was transported to the Fairyland – Avalon, where he is healing his wounds in serenity.
Saber’s ability is maximally unleashed while engaging in an honourable face-to-face single combat. It is a method of battle that is full of chivalric honour, and it is also one that suits Saber's sense of aesthetics. However, this does not mean she dislikes strategising. Because she is also a capable military commander, she tends to loath fabricated strategies that have no concrete basis. She fine-tunes her strategy meticulously. While on the battlefield, she further adapts her actions in response to the ever-changing dynamics of combat. Naturally, Saber despises cowardly actions, strategies or not. For this reason, in the Fourth Holy Grail War, her compatibility with the cool-headed, achieving-his-goal-at-all-cost Master Emiya Kiritsugu was the worst.
Magic Resistance: A
Artoria boasts the highest rank of resistance to magic amongst the Servants. She is capable of completely neutralising grand sorceries involving magic arrays and instant contracts. Even modern magi of the highest level cannot wound her directly with sorcery. Artoria is able to resist an action force onto her powered by one stroke of the Command Spell. Such is the extraordinary rank of Artoria’s Magic Resistance, sufficient to shake the very foundation of the Servant System. If the opponent is someone who attacks with sorcery, Artoria will charge without fear and determine the outcome of the battle with a slash.
Also, as her “Pendragon” name shows, Artoria is the holder of the Element of the Red Dragon, charged with the task of protecting the kingdom. She carries the very magical power of the Dragon. This humongous magical power is also the source of Artoria’s Magic Resistance. Due to the characteristics of Dragon, Artoria has much trouble with existences such as Siegfried, who is associated with tales of “Dragon extermination”. If she is targeted by “Dragon-slaying Sorceries”, it is possible that Magic Resistance will not function to its fullest extent.
In the story, Artoria retained her Magic Resistance of A while having Emiya Shirou and Rin as Masters, regardless the two’s differences in power and characteristics. On the other hand, while having Matou Sakura as her Master, her Magic Resistance decreased to B as a result of Blackening.
Since “knights” are soldiers who are proficient in mounted warfare, Saber’s rank in Riding is very high. Chariots can be ridden the same way. Motorcycles and automobiles are treated as “modern mounts”, thus a high rank in Riding is also applicable. It is unclear if Riding is applicable to aircrafts. Saber’s Riding was elevated to A while having Emiya Kiritsugu as Master. However, Artoria can ultimately only control normal mounts. She cannot control Pegasi, Griffons, Dragons, and other Magical Beast, Divine Beast Ranked Phantasmal Species. This is due to her Class not being Rider, as well as the fact that she was a King in the Age of Man, thus did not have the fortune of having “Legends of Riding Phantasmal Species”.
Artoria rode a motorcycle in the Fourth Holy Grail War, but did not have the opportunity to demonstrate her Riding ability in the Fifth Holy Grail War. Provided with the appropriate mount, the battles might have developed differently.
Instinct is the ability to instantly identify “the best personal course of action” during combat. Because this skill allows for the prediction of trajectory, it is possible to avoid attacks from firearms. At rank A, it is essentially in the realm of predicting the future. Through this ability, it is possible to negate the penalties inflicted by visual and auditory interference to a certain extend.
Being able to discern Cú Chulainn’s ultimate technique certainly reflects her skills, but having exceptional Instinct also helped her immensely.
Mana Burst: A
The ability to reinforce one’s weapon and body through the infusion of magical energy. By reinforcing the ability of the body to a great extend using magical energy, the physically fragile Artoria was able to fight head on with monsters such as Berserker. At rank A, even a stick can become a weapon of great power.
Executing large-scale body reinforcement through Mana Burst is only possible with Artoria’s immense magical power.
(Translator's Note: This is basically analogous to Strengthening/Reinforcement Sorcery.)
Artoria possessed high Charisma, and reigned as the king of England. The morale of military forces she commands is extremely high. However, this strong influence is still insufficient to build a vast empire spanning the world, so it remains at rank B (enough to rule a country).
Caption: Artoria, the protector of the British Isles. Even with her Charisma, she could not avert the fall of her kingdom.
Maximum Targets: 1 Object
A barrier that renders the blade hidden by entangling it with layers of wind, and altering the light refraction rate. It is closer to a sorcery than a Noble Phantasm. By using this barrier, Artoria can attack without the opponent recognising the sword’s reach and trajectory. Since concealing one’s Noble Phantasm also conceals one’s true identity, Invisible Air was highly effective at the early stages of the Holy Grail War. It also has other advantages such as increasing attack power and accuracy. Entangling the sword with wind and using the wind as the blade enhances the attack power, while having an “invisible weapon” provides an advantage in accuracy. (Translator’s Note: It is probably more “decreasing opponent's evasion” in RPG terms.) Since the advantage of Invisible Air lies in “invisibility”, the accuracy increase will not occur while engaging opponents who possess Eye of the Mind or do not depend on vision.
In the Fourth Holy Grail War, Artoria unleashed the condensed air and used it as a long-range weapon that mauls down groups of enemies --- “The Iron Mallet of the Wind King”.
Maximum Targets: 1000 Persons
The greatest and most powerful Noble Phantasm of Artoria (Translator’s Note: Not Avalon?). It is the strongest and most majestic holy sword that symbolises King Arthur. The pinnacle of holy swords. Excalibur was not forged by mankind, but crystallised within the Earth, using the wishes of mankind as the basis. It is one of the ultimate God-forged weapons, a Last Phantasm. Originally cared for by the Faeries of the Planet, it was passed into the hands of King Arthur through the Lady of the Lake.
Excalibur converts the mana of the wielder into light, and as the sword is swung, the light is released from the tip of the blade like a laser beam and destroys everything in its path. Of course, the mana consumption is extreme, thus it cannot be fired consecutively. In the Fourth Holy Grail War, the beastly giant sea monster summoned by Caster was completely incinerated by this Noble Phantasm. Excalibur is classified as an ‘Anti-Fortress Noble Phantasm” due to its magnitude and destructive power.
Type: Bound Field
Maximum Targets: 1 Person
The sheath of Excalibur, a Noble Phantasm with its origin in the Fairyland Avalon where King Arthur rests. The wielder will heal from any wound, and the aging process will cease. Unleashing the true name of Avalon will deploy a Bound Field that provides the greatest defence. A Noble Phantasm that annuls the interference of True Magic; its existence is equivalent to True Magic.
In legend, losing this sheath casted an ominous shadow onto the life of King Arthur, eventually cascading to the collapse of the kingdom. In modern times, the Einzberns excavated Avalon at Cornwall and passed it into the hands of Emiya Kiritsugu. Afterward, it was planted into the body of Emiya Shirou to save his life, eventually becoming the link that led to his bond with Artoria. In Fate Route, Artoria learned that Shirou was her “sheath”, which led the duo to emerge victorious in the Holy Grail War.
 Fate/Zero material - Servant Status: Saber, p.012-013
Master: Kiritsugu Emiya
True Name: King Arthur
Alignment: Lawful Good
Noble Phantasm: A++
■ Magic Resistance: A
Cancels all magecraft below A. In reality, no magi of today can harm Saber.
■ Riding: A
Able to freely manipulate all beasts and vehicles, save mythical beasts and divine beasts.
■ Instinct: A
The ability to always "feel" the best course for oneself during combat. This heightened sixth sense is now close to precognition. It reduces by half any obstacles to vision and hearing.
■ Mana Burst: A
This transfers magical energy into one's weapon and body, and by releasing the magical energy instantaneously, it increases one's ability.
■ Charisma: B
Natural ability to command an army. Charisma is a rare talent, and B-rank is enough to lead a country.
■ Invisible Air: Bounded Field of the Wind King
Type: Anti-Unit Noble Phantasm
Maximum number of targets: 1 person
An invisible sword. Simple, but displays tremendous effect in hand-to-hand combat. A Noble Phantasm guarded by strong magecraft, it does not mean the sword itself is transparent.
■ Excalibur: Sword of Promised Victory
Type: Anti-Unit Noble Phantasm
Maximum number of targets: 1 person
A sword of light. A weapon not made by man, but a god-made equipment forged by stars. A Noble Phantasm at the top of the category of holy swords. A holy sword which transforms the owner's magical energy into "light", increasing its momentum due to the convergence and acceleration, and enable the use of magecraft of divine levels.
■ Avalon: The Everdistant Utopia
Type: Barrier Noble Phantasm
Defense target: 1 person
The power of the sheath of Excalibur. Expanding the sheath, it shuts out all physical interference by placing the owner in the land of the fairies.
 Fate/complete material III: World material - FAQ with Nasu: Noble Phantasms, p.134
Q: What did you have in mind when you created these original Noble Phantasms (“Bounded Field of the Wind King: Invisible Air”, “All-Violating Talisman: Rule Breaker”)?
Q: Though many Servants possess Noble Phantasms that appear in their actual myths and legends, there were some that felt like original creations for the game. What did you have in mind when you created these original Noble Phantasms (“Bounded Field of the Wind King: Invisible Air”, “All-Violating Talisman: Rule Breaker”)?
A: Invisible Air was simply a form of sorcery meant to conceal a Noble Phantasm. I thought that surely Merlin could have managed that somehow! Heroic Spirits that possess overly famous Noble Phantasms have a trick or two to hide their true identities.
[As for Rule Breaker,] I created it from her image as a treacherous archmage. I figured she would be too weak with only her Dragon’s Teeth soldiers.
- Fate/Grand Order material IV - Artoria Pendragon (Lancer), p.080-089, translated by Clyton at Beast's Lair.
- Fate/Grand Order material III, section on Artoria Pendragon (Lancer) (Alter)'s Noble Phantasms, translated by You at Beast's Lair.