Clarent: Radiant and Brilliant Royal Sword (燦然と輝く王剣, Sanzen to Kagayaku Ō-ken?) is Mordred's sword, originally stored away by King Arthur in the armory of CamelotWP. Described as "more dazzling than any silver", it is an ornate, sparkling white silver sword adorned with splendid decorations, acting as a symbol of kingship denoting the right of succession of the throne. It is a treasured sword that has worth equal to, if not exceeding, Caliburn, that amplifies the authority of the king, the "king’s royal aura." It thus raises the owner's physical parameters by one rank and grants and raises the rank of the Skill Charisma.
It is normally a B-rank sword bestowed during the succession of kingship, but Mordred stole it without acknowledgement. She obtained it by breaking into the vaults of Camelot upon temporarily claiming the throne during her rebellion after inciting the incidents that drove her father to lead an expedition after the traitorous Lancelot. Due to this action, she was never acknowledged as a king, so the rank of the sword is lowered by one rank to C and does not grant her any of the normal bonuses while she wields it. She still came to favor utilizing it due to it being a "sword that symbolizes royalty" and can still utilize its ability of "amplification". As an application of Mana Burst, she is able to drive her excessive hatred into the sword and amplify it to utilize Clarent Blood Arthur.
In Fate/Prototype: Fragments of Blue and Silver, it is revealed that the sword Florent, wielded by Lucius Tiberius, is a brother sword to Clarent. It is also said to indicate the King's rule over Gallia in contrast to Florent indicating the Emperor's rule over all the people of the continent.
Clarent Blood Arthur: Rebellion Against My Beautiful Father (我が麗しき父への叛逆, Waga Uruwashiki Chichi e no Hangyaku?) is the full power, released form of Clarent utilized by Mordred, a transformation into an evil sword of hatred upon the condition of her holding it. It is not the proper nature of the sword, but an effect of the episode in Mordred's legend where she had stolen the sword from King Arthur's armory and then later used it to deal a fatal blow to her father. It is an application of Mana Burst that allows her to force her excessive hatred for her father into the sword in the form of magical energy, and then the sword amplifies it and allows it to be launched as an attack. It manifests red lightning, her twisted feelings for her father that have been amplified by the sword, and directs it at the opponent. Mordred feels the weapon possesses a "curse‐like glory", not allowing herself to be defeated by anyone who is not her father, and even more so, not permitting for the sword that delivered a fatal blow to her father to fail in killing an opponent. Compared to the pride felt by other Heroic Spirits, it being crowned with the name of her father makes it more akin to a grudge in Mordred's case. Should she make peace with her discord towards her father, even one-sidedly as in the Great Holy Grail War, she can still launch the attack regardless of her feelings towards her father as an innate talent inherited from the blood of the King of Knights.
Upon utilizing it, she takes a stance, while at the same time, her helmet, Secret of Pedigree, is removed due to the requirement of it being released before she can use the attack. The space around her and the sword becomes stained with dark red blood, and the blade of the sword, enveloped by the radiance of blood, gives off strange, violent and furious sounds and begins to transform. Changing from Clarent's normally pure and beautiful form, her great hatred transfigures the sword into that of a sinister and wicked blade befitting a demon, a "demonic sword of calamity". Transformed into a grotesque and unsightly form, red lightning flickers through the surroundings as it is clad in her wanton hatred. Upon raising the sword, she releases the blood radiance upon the enemy as a flash of light, a surging wave with the simple purpose of destruction. It releases a straight line of crimson lightning from the tip of her sword, destroying all in its path. Utilizing it takes a great deal of energy, giving her intense pain throughout her body, but her Master's competency allows her the strength to move immediately after utilizing it.
Noble Phantasm: A
■ Magic Resistance: B
Cancel spells with a chant below three verses. Even if targeted by High-Thaumaturgy and Greater Rituals, it is difficult for her to be affected.
■ Riding: B
Most vehicles can be handled with above average skill. However, cannot ride the likes of Phantasm Races such as Monstrous Beasts.
■ Instinct: B
During battle one is able to always feel the optimal course.
Visual and auditory obstacles are halved.
■ Mana Burst: A
Weapons and body are infused with magical energy, this instantaneous release elevates ability. In other words, magical energy as jet propulsion. With this is able to fight equally with the King of Knights.
■ Battle Continuation : B
Doesn't know when to give up. Did not give up even when pierced with a Holy Spear and ended up giving the King of Knights a mortal wound.
■ Charisma : C-
Natural army commanding talent. During team battles one's team's abilities are elevated. A rare skill.
Mordred's charisma fully shows itself during during rebellion.
■ Secret of Pedigree: Helm of Hidden Infidelity
Type: Anti-Unit (Self) Noble Phantasm
Range: 1 Person
Maximum number of targets: 1 Person
The helmet her mother Morgan gave to her along with the words "You must not remove." Within the Status, personal skills, Noble Phantasm and anything connected to the True Name is masked. However when Clarent: Radiant and Brilliant Royal Sword is released, the helmet must be removed.
■ Clarent: Radiant and Brilliant Royal Sword
Type: Anti-Unit Noble Phantasm
Maximum number of targets: 1 Person
The sword denoting the right of succession of the throne that was stored in King Arthur's armory. It is described as "more dazzling than any silver, and is a treasured sword with worth excelling or at least not inferior to "The Golden Sword of Promised Victory." Because Mordred stole the sword without acknowledgement, the rank is lower than the original.
■ Clarent Blood Arthur: Rebellion Against My Beautiful Father
Type: Anti-Army Noble Phantasm
Maximum number of targets: 800 People
Clarent's full power released form. Original was an ornate, sparkling white silver sword, but when invoked it is dyed with dark red blood and warps into an unsightly form. The blade is clad in wanton hatred and fired. A demonic sword of calamity.
Radiant and Brilliant Royal Sword [Noble Phantasm] Rebellion Against My Beautiful Father [Noble Phantasm]
Clarent Blood Arthur.
Together, they are Mordred’s Noble Phantasm. It was originally a sword stored in King Arthur’s treasury. But Mordred broke into the treasury when she caused her rebellion. Perhaps being interested in it as the “sword that symbolizes royalty”, she came to favor using it.
It was originally a B rank sword bestowed during the succession of kingship, used to amplify the king’s authority… the king’s royal aura. Concretely, it raises the owner’s physical stats by one rank, and grants and raises the skill “Charisma”. However, since Mordred was never acknowledged as king, the sword itself is lowered by one rank and she cannot acquire any bonuses while wielding it.
However, the ability of “amplification” itself has not been lost, so Mordred drives her excessive hatred into the sword in the form of prana, thereby amplifying it and allowing her to shoot it as an attack.
To make it easy to understand, “Clarent Blood Arthur” is an application of “Prana Burst”, and the red lightning that it manifests are her twisted feelings towards her father that have been amplified by the sword.
In the light novels, her discord with the King of Knights was (one-sidedly) resolved, but she can still shoot it regardless of her feelings towards her father. In that regard, she possesses the innate talent inherited from the blood of the King of Knights.