Similar in age to Shido, Kaguya and Yuzuru are identical twins, even being described as "clones" since they both split from the same Yamai Spirit, with the reason for the split as well as the original Yamai's personality both being unknown. Although they are two different, independent individuals, strictly speaking they are still one Spirit, Yamai. They both have long orange hair and mercury colored eyes. They are well known to people who know about Spirits as well as the general population due to causing a major atmospheric change when they duel while having a significant amount of witnesses. However the spacequakes they cause have few to no casualties due to them manifesting high up in the sky. Their constant duels stem from both of them arguing about who is the real Yamai. Both of them have dueled in various fashions, with 25 wins apiece and 49 draws after 99 matches. On seeing Shido they agreed their 100th and final match to be who can seduce him first, with the winner being the real Yamai, and the loser disappearing.
However deep down they each wanted the other to live, resulting in the both of them asking Shido to choose the other. When they learned of each others true thoughts, they got angry enough at each other for not wanting to live, to fight again, this time to see who would run out of energy first and thus die. However Shido managed to stop them and give them the option of both living on as Yamai, as well as him sealing both their powers together. They both realized that what they really wanted, was for both to live on together. Being grateful to him for giving them that option, they kiss him together, which seals their powers. They join Shido's school, transferring to class 2-3, the class beside Shido's. Their relationship is close enough to count as lovers rather than just sisters.
Their Angel is Raphael, whose true form is a bow and arrow weapon, El Kanaph, which has a high penetration capability, and is formed by combining their weapons. They both possess the power to control air currents. Their Astral Dresses, Elohim Tzabaoth, are visually masochistic, being covered in a dark colored coat with various parts of their bodies being covered by straps, Yuzuru's being blue. Both also have locks which possess torn off chains protruding from them, Yuzuru's being on her neck, left hand, and left leg. Their AST codename is Berserk.
Personality-wise, she speaks in a distinctive manner in an almost robotic structure with her intent of the statement stated beforehand in a one word sentence. She is reserved however she will not hesitate to point out the flaws within Kaguya's arguments. She looks identical to Kaguya, albeit being slightly more well-endowed than her twin. Other differences include her hair being braided into three portions and her expression appears listless. Her main weapon is El Nahash, a pendulum.