Gáe Bolg

Gáe Bolg (ゲイ・ボルク) is a cursed spear that was obtained from Scathach in the Country of Shadows by Cú Chulainn. Scathach had wished for him to slay her with the spear, but she had already ceased being mortal by the time he received it from her. It is a glory given to only the most gifted of warriors, and it was not utilized once after he left the Land of Shadows until his fight with his close friend, Ferdiad. He later used it again on his son, Connla, when he was backed into a corner during their fight. The spear leaves behind but one regret: that it has only taken away the lives of his loved ones. It killed his one and only close friend and his son that grew up in a distant land, even though it was meant to have killed one woman before them.

It is unique in that it functions in two different ways, each different enough to have them be treated as separate Noble Phantasms. The Anti-Unit thrusting technique of the spear is the main offensive ability he utilizes, but the Anti-Army throwing ability is the spear's true function as a throwing weapon. It is descended from : The Declaration of the Elder God, which belongs to Odin in Norse mythology, and Brionac: The Five Roaring Stars, the lance of the Celt god of light and Cú Chulainn's father, Lugh.

Barbed Spear that Pierces with Death
Gáe Bolg: Barbed Spear that Pierces with Death is an attack focused on a single target, created by Lancer to suit his own style, that strikes a fatal blow that always pierces the opponent's heart and ruins their body from within with its thousand iron thorns. It literally freezes the mana in the air, and it can easily be perceived as a sure-kill technique by all those around simply from being charged with prana. Once Gáe Bolg's name has been called, the cursed spear reverses the nature of causality, the meaning of "cause and effect" in the order of things, to make it so the cause of the "lance being thrust" comes from the effect of the "opponent's heart being pierced" by it. It determines the opponent's fate simply through its use, an always fatal move that pierces the heart with one thrust. It is also possible for him to activate it without actively striking the heart.

The actual action of the thrust is merely a formality, as the lance has already pierced the opponent's heart before the attack has even started. The "result" of "the heart of the opponent has been pierced" is created earlier than it is thrust, while the "cause" that "the lance has pierced through the heart" is generated later. Aside from great luck, it is a technique that determines "if it is released, the opponent is dead." Its range of effectiveness and power are weak compared to its other ability, but it has a low energy cost. Even with its nature of interfering with destiny and effect of "almost certainly will destroy the enemy's heart", the attack only utilizes prana in the double digits compared to a single spell from Caster costing hundreds of units of prana, and each activation is a sure kill, making it one of the most efficient Noble Phantasms with extraordinary usability that can be used up to seven times before Lancer must obtain more prana from his Master.

The lance can move at impossible angles, signified by turning into a red beam of light, that always manages to reach its target. Even if he thrusts directly at the feet of the opponent, such as in the battle with Saber, it will immediately point upwards towards the heart without growing, bending, and or any movement from Lancer, and if it is thrown from a distance of ten meters, or rather than truly being a throw, "Lancer's own body is fused with his soaring spear", it will change its path around any obstacles or pierce through any wall in order to reach its target. This action looks completely normal to onlookers, as if it it were already piercing the heart, because rather than truly changing its course, it changes the means to match the result, simply as an action meant to prove the fact that the heart was pierced. It can only be used against living beings, so it would have no particular effect against inanimate objects like rocks or houses.

The lance curses the target upon striking them, delivering wounds that cannot be healed while Gae Bolg still exists in the world. While Lancer mentions that even a regular thrust through his heart would be hard to heal, being struck by the Noble Phantasm gives the greatest effect. As the "lance of cause and effect", it curses them, leaving them unable to change their fate without great luck. Those who are cursed will bear the wound until they die unless Lancer is killed or the spear is destroyed. Saber is only able to heal her wound on the outside, while she is able to fully heal a much greater wound from Berserker in a matter of hours, and she is plagued by it for weeks afterward. Shirou is able to recover slightly with Avalon, but the wound still persists until Lancer's death. Its curse is no longer effective against him with the scabbard's protection, but it takes over half a day to heal even with its potent regenerative abilities.

The attack delivers damage equal to the opponent's own health limit plus the damage from the spear itself, so the wound will be fatal no matter the opponent once they are struck. If the target has "100HP", the attack will deliver "the damage caused by the spear + 100", making it a surety that they will die. This makes it especially effective against those with high durability, even those who can survive being hit by Excalibur. Even someone like Arcueid Brunestud, who is very much superior in numbers compared to Lancer would be killed as long as she wasn't saved by her luck. There is a small disadvantage against Servants who can move around even without their hearts like Heracles. The wounds from its attacks are rather clean, spilling only a small amount of blood compared to a regular wound of comparable size, and while a heart would normally explode from such a strike, it instead stops working with the singe strike.

It is like Tsubame Gaeshi in that the best measure against it is to not allow it to begin. Unlike Tsubame Gaeshi, which there is no way to stop once it has been used, it is possible to find a countermeasure for Gae Bolg once it is found out that it will go for the heart. It is impossible to dodge the thrust of the lance, no matter how agile, well guarded, or far away from the lance the opponent is standing. Even having EX rank agility would be useless, so the only benefit would be allow the opponent to back out of the attack's range before it is initiated. While it would normally be ineffective against Berserker's God Hand, Lancer could take at least one of his lives by using his runes to power up the rank of the lance to A to bypass God Hand's nullification ability.

The only way to effectively defend against the attack is to have a high enough degree of luck or divine protection as to be able to alter fate, which would be heightened by also having good reflexive instincts, an auto-resurrection ability, a shield that overwhelms the magical energy of the lance, or, as a countermeasure of knowing it will strike the heart, by following Archer's strategy of quickly backing out of the attack's range before it is initialized. Even if the opponent manages to avoid it with luck, as with Saber, it still leaves a heavy wound on her that takes a long time to fully heal.

The conceptual strength behind it is strong, so it will clash with something like Fragarach. Even if Lancer is killed and the attack is nullified by returning it to before it was activated, such as when going against Fragarach's unavoidable counterattack, the lance's curse will wind back to the moment "Gáe Bolg" was chanted in order to carry out its purpose of striking the heart. Fragarach alters the order of events, but Gae Bolg reverses cause and effect. It has already pierced the heart as the result, so even its master's death will not impede it from fulfilling its duty. The two opposing laws clashing against each other leaves both Lancer and Bazett dead afterward.

Soaring Spear that Strikes with Death
Gáe Bolg: Soaring Spear that Strikes with Death, which is the true use of Gáe Bolg, is the largest and most powerful attack delivered using the spear. It is the “attack that unleashes countless darts at the enemy” that is spoken of in the legends. It is the attack that made him a hero which utilizes the full potential of the lance's curse, converting all of Lancer's prana into energy and releasing the accumulated power after the spear is hurled, detonating on impact with enough power to blow away a multitude of enemies.

Lancer prepares to use this ability by backing one hundred meters away from his opponent, taking a crouching position on all fours, and accelerating through an approach run by dashing fifty meters before taking to the skies. He arches his back as if drawing a bow and hurls it towards the ground with all his might. It distorts space to create a "tapestry of action" that splits into numerous spearheads that pour down over the enemy. It is said that it split into thirty in his legend, but it seems that the number has increased after Cú Chulainn became a Heroic Spirit. Compared to the very little usage of prana with the anti-unit technique, this ability has an intense consumption of energy.

It does not carry the property or concept of “always pierces the opponent’s heart”, but both the power and the area of effect are increased. Rather than dispatching a single foe with absolute accuracy, its focus as a technique is to attack the enemies together with the surrounding area in a carpet bombing fashion to cause massive destruction. Due to being hurled with all of his energy, it cannot be dodged or blocked under normal circumstances. Even resilient bulwark or agile body are not immune to its power, so Gáe Bolg will send the enemy horde flying. If it were to also have the ability to directly strike the heart, it would be closer to the level of Lugh's power as a higher level version of Fragarach. The idea that Archer is capable of blocking it with Rho Aias after the spear pierces through the first six layers seems impossible to him.

The form and damage caused come close to Lugh's Brionac, but having the ability "No matter how many times it is dodged, it will strike the enemy" makes it a Noble Phantasm closer in nature to Odin's Gungnir. Archer comments that it surpasses the original Gungnir in power, and that out of all the spears he knows, it is the only one able to pierce more than one layer of Rho Aias. The spear travels at mach two, and the farthest he has thrown it is forty kilometers. Shirou believes that his actual range could extend to the other side of the Earth. Lancer thinks only two other people, three conditionally, in the world could beat that record.