Kanshou and Bakuya

Kanshou and Bakuya (干将・莫耶) are "married" twin swords representing yin and yang encountered by Archer at some point during his lifetime and added to the numerous weapons recorded and stored in Unlimited Blade Works. They are his favored weapons to project, having become his symbols after wielding them all his life. He and Emiya Shirou find the craftsmanship of the blades, rather than what they represent, to be extremely captivating and beautiful, and the swords suit their natural style of fighting. Despite not having a wielder in the legends, they are still Noble Phantasms crafted by the blacksmith Gān Jiàng, whose wife, Mò Yé, gave her life in order to melt the metal used to create the swords during the Spring and Autumn Period. They were crafted more for the sake of crafting, as if questioning the meaning of the swordsmith, than for any real idea behind their creation. They were created without vanity, and lack a sense of purpose found in other swords. They contain no fighting spirit to defeat others or competitive spirit to beat other weapons, and they contain neither the desire to be famous nor the faith to accomplish great deeds.

They are identical in shape with the only difference being their color. Kanshou, the black Yang sword, is covered in a hexagonal pattern, and Bakuya, the white Yin sword, has less of the shine of a polished metal in its ore than it has the haze of a cloud. Their quality as swords is high due to being made with the best materials and a human sacrifice, and they have shamanistic and ritual aspects as enchanted weapons. The quality of the grips, which are quite big and heavy, are more important than their ornamental value. They are rather low ranking compared to other Noble Phantasms, but the dual-wielding style, their experience, and their tracing time make them very reliable. The main ability of the swords is their strong bond with each other, which not only allows them to attract each other, but it is also said they will return their owner even if events cause them to be lost. If one is thrown while the other is held, the thrown sword will return to the wielder much like a boomerang. This works well with projection, allowing an already projected sword to identify a new projection as its partner sword. When both are wielded, magic resistance and physical resistance improve. The original versions of the swords that reached the realm of the Gods due to human sacrifice, rather than the imperfect projected versions, also have a strong affinity against monsters, allowing them to easily cut down creatures like the Gorgon form of Medusa and the extradimensional evil god summoned by Caster in a single strike.

Chant
Words that seem like anti-demonic charms carved onto the blades have been added by Archer. The true meaning behind the words has nothing to do with the ideology behind the creation of the swords, but rather the foundations of his swordsmanship. It also represents Crane Wing Three Chains (鶴翼三連), a strategy that is the cumulation of Archer's use of the swords, the true meaning behind them, using three consecutive pairs traced ahead of time and the pair of swords' attraction to each other to deliver a fatal attack by projecting them when necessary. The main usage of the attacks is three consecutive X-shaped strikes, though the version used by Shirou after obtaining information from Archer's arm in Heaven's Feel is different.

In Archer's version, the first pair is thrown at the enemy with the purpose of being deflected, while the second is prepared for close range combat. While the enemy is off guard, he slashes with the second pair, and the thrown pair returns and hits the enemy from behind. Finally, the third pair is modified through reinforcement, called Overedge, which makes them twice the size and covers the blade from the ridge to the edge with feather-like splinters, and he performs the final strike with them. The design for Overedge comes from the animated version of the fight between Archer and Berserker, and was created by the art director anime, Koyama Toshihisa. Nasu Kinoko fell in love with the dangerous look of the swords, and applied them to Archer's version of the attack in reference material.

Shirou's version used to defeat Saber Alter begins with a thrown pair aimed at the neck, coinciding with the first line of the chant, that is deflected by the enemy, and then closes in for close combat with a second pair. The thrown Bakuya returns from behind to attack the enemy and he immediately strikes with the Kanshou in his hand. Directly afterward, the thrown Kanshou returns and he uses the Bakuya in his hands to attack as well, coinciding with the second and third lines. Saber managed to block all four attacks, but the result left her defenses completely open. He then projects the final pair without any reinforcement to slash the enemy's open defense in a downward X-motion, coinciding with the final two lines. It is a essentially a methodical strategy at rendering the opponent defenseless.