|Spoiler Alert: This article/section contains details about future plot lines described in the light novels, not covered in the anime. Do not proceed unless you want to be spoiled.|
|“||I don’t want to die…I want to live…I, I want to be with Yuzuru more.||”|
|“||Reply---Yuzuru….too. I don’t want to disappear. I want to live with Kaguya.||”|
Yamai was originally one Spirit, but for unknown reasons that may be related to her teleportation between dimensions sometime in the past, she was split into two bodies and minds. The original personality of Yamai is now gone, as well as what type of character she used to have is unknown to the split Yamais. The Yamai Sisters have been well known to the people who knew about the existence of Spirits because they often cause a major storm in an area, which occurs every time they come to Earth.
It was unstated when the Yamai Sisters started fighting, but they have been fighting with each other for quite some time for the sole purpose of deciding the winner as the real Yamai. Their matches range from non-violent to violent for almost 99 battles with the 100th battle as the final confrontation. Whether out of luck or by chance, the Yamai Sisters encounter Shido while he and his classmates were having a field trip to the southern island; the Yamai Sisters decided that their 100th battle should be whoever can seduce Shido first will be the winner and will be considered as the real Yamai. It was around this time, thanks to Reine, which the Yamai Sisters transfer into Shido’s high school and the beginning of both Yamai sisters and Shido's battle to seduce each other.
In reality, both of the Yamai Sisters secretly wanted the other to live, but when they discovered that both of them have the same idea, they stubbornly refuse themselves to live and for the other to die; so in the end, they fought. Thankfully, Shido forcefully interrupted their fight with Tohka’s sword, Sandalphon, and gave them a new option for both of them to live and that is for him to seal their power. They pondered on that idea until they finally accepted their wish to live along with each other. Both of them got their power sealed at the same time when they gave Shido a thank you kiss.
Due to their stable mental state after being sealed, they didn't need to transfer into Shido's classroom, but the one next door to his.
Being identical twins, Kaguya and Yuzuru look almost the same. They both have orange hair and blue eyes and appear to be of the same height. However, watching carefully, both still have their individual characteristics.
She has "a characteristically delicate body that looked like it would break if hugged too tightly" as described by Shido. Her hair is braided up, and she has a lean figure. She has a determined expression for most of the time. Kaguya's Astral Dress is mainly the color purple and has chains on her right hand and foot. The lower half of her body has a half skirt around her waist which drops to the knees and opens around her thighs. Kaguya's height is stated to be 157cm, and her three sizes are B79/W56/H81.
She has "the body of a model" as described by Shido. Her hair is braided in three portions, and she has a curvy figure. She has a vague expression and keeps her eyes half closed for most of the time. While her sister's Astral Dress is mainly the color purple, Yuzuru's dress is bluish-purple with a small cape and has chains on her left hand and foot. Yuzuru's height is stated to be 158cm, and her three sizes are B90/W61/H86.
Despite being twins, their personalities are almost complete opposites to each other.
Outgoing and outspoken, one can say that she is childish or immature. Kaguya often speaks rather unrealistically, as if she is acting. It is later revealed that it really is acting. Kaguya believes she needs to talk like this because she is a Spirit, and therefore "super awesome", and therefore must act appropriately. But her acting can be easily broken if pressed upon, and because of this, she's constantly being teased by others around her. She's also weak about sensual matters and is easily embarrassed when mentioned.
She often speaks in a robot-like speech pattern; when arguing with Kaguya, Yuzuru always sneers at her and points out the flaw in Kaguya’s argument. She tells the point of comment before speaking the rest. For example, "Confirm; Shido". She sometimes speaks in the third person.
Yamai Kazamachi was born a vanishing twin, with her absorbing her stillborn twin while still in ureto. She grew up to become an ordinary high school student heavily involved in anything she could participate in like music and athletic activities. One day, around at the age of 17, she saw a child that was about to be hit by a vehicle. Wanting to be like a hero she always admired as a kid, she moved to save the kid at the expense of being struck in that child's place. As her consciousness started to fade, Mio appeared and gave her a Sephira Crystal to save her life. However, rather uniquely the Sephira reacted bizarrely with the DNA of her stillborn twin sister as well, causing the original Yamai Kazamachi to split apart into two. The subsequent twins Kaguya and Yuzuru then both inherited different aspects of the original's personality and preferences. Over time both twins came to forget about their human life, only remembering that they both originally came from one Spirit called Yamai.
The Yamai Sisters subsequently became well known to the people who knew about the existence of Spirits because they often cause a major storm in an area, which occurs every time they come to Earth. It was unstated when the Yamai Sisters started fighting, but they have been fighting with each other for quite some time for the sole purpose of deciding that the winner will become the real Yamai. Their matches range from non-violent to violent for almost 99 battles, with them deciding that the 100th contest will be their final confrontation.
- Light Novel
- Volume 5-22
- Date A Live Encore 1-10
Powers and Abilities
Due to having their Sephira Crystal split in half between each other, both twins share the same powers commanding wind. In terms of speed, they are regarded as the fastest Spirits. After hearing that they were originally one being, Reine theorizes that Kaguya and Yuzuru have their own unique Path that circulates Reiryoku between the two of them. She compares it to the Path which Shido establishes after sealing a Spirit.
Both of the Yamai Sisters, despite using different weapons; have the power to manipulate wind. They can gracefully control the air currents in order to glide through the sky. At their full power, both of them can easily create a typhoon that can blow away a small island. They also have shown to be able to combine their powers to form a bow and an arrow that is able to pierce through the <Arbatel>'s Territory.
- Kaguya: El Re'em (
穿つ者, Ugatsu-mono?. lit. "Piercer")
- Yuzuru: El Na'ash (
縛める者, Imashimeru-mono?. lit. "Constrictor")
- Combination Attack: El Kanaph (
天を駆ける者, Ten o Kakeru-mono?. lit. "Sky Rider"): A single decisive blow fired from a combination of the Yamai sisters' individual Angels. Both of their wings combine to form the body of the bow, Yuzuru's pendulum becomes the bowstring, and Kaguya's lance becomes the arrow.
After being forced to see Ellen kill Shido on the school rooftop, both of the twins, along with Tohka and Origami, assumed their inverse forms due to the overwhelming despair in their hearts. In this form, the Yamai sisters were both surrounded by a tornado that indiscriminately rampaged around the buildings beside the school. However, the status quo was restored after Kurumi used the sixth bullet to travel back in time.
Upon taking in Beast's Eighth Sword, both Kaguya and Yuzuru grabbed the spiral blade at the same time, causing their bodies to temporarily merge and fuse as one. In turn, this causes a recreation of the original Yamai Kazamachi to be reborn. However, Yamai considers herself different than the human Yamai Kazamachi due to the personal growth that both Kaguya and Yuzuru have developed after splitting apart. The fusion grants enough strength to overpower Beast after she had already been weakened by Origami and Kotori's attacks. However, as a forced fusion, there is a time limit set before both Kaguya and Yuzuru are forcibly split apart again, which does occur shortly after their fight with Beast concludes. Nevertheless, their fusion allows Yamai access to <Raphael>'s full power, combining Kaguya and Yuzuru's individual weapons together for various defensive and offensive purposes.
- (To Shido Itsuka) "……………It's better if I don't know right………then, I'll believe you. That's because, Shido was the one who gave me and Yuzuru the 3rd choice at that time……………." 
- (To Shido Itsuka) "Convinced. Kaguya is often like that but, she really loves Shido. There is no mistake since Yuzuru says this. Yuzuru and Kaguya were originally from one body and one soul. What Yuzuru hates, Kaguya also hates. Similarly---------what Yuzuru loves, Kaguya also loves." 
- Yamai was the original Yamai Kazamachi's given name. However, after splitting apart, both Kaguya and Yuzuru adopt Yamai as their shared surname.
- Kaguya and Yuzuru have fought each other for 99 times. The results are 25 wins, 25 loses, and 49 draws.
- Yamai has the "Eight" character in her name (「八」舞). It refers to eighth Sephira on the Kabbalah's Tree of Life: "Majesty or Splendor."
- Fitting their respective Angels' roles in Raphael's bow form, Kaguya's name contains "arrow" (矢, ya) and Yuzuru's name contains "bowstring" (弦, tsuru)
- Oddly Kaguya and Yuzuru's angel is supposed to be Michael because Raphael governs the sixth Sephira on Kabbalah's Tree of Life, "Beauty," while Michael governs the eighth Sephira on Kabbalah's Tree of Life, "Majesty or Splendor."
- However, Raphael and Michael are said to co-operate on the governing of the 6th and 8th sephirot, therefore both can be said to be affiliated with those sephirot. The fact there are two Yamai spirits likely illustrates the point that it has two governing entities.
- The Yamai sisters' Astral Dress's name is 'Elohim Tzabaoth' which means "God of Hosts or Armies." (Derived from the two Hebrew word: "Elohim" Which means God in Hebrew and "Tzabaoth" a Hebrew word which means "Host" or "Armies").
- Their angel, Raphael's name means in Hebrew was "God has healed" or "God's healer," Which "Raphael" was one of the Seven Archangel that appeared in the Book of Tobit.
- The actual meanings of El Re'em (ראם), El Na'ash (נחש), and El Kanaph (כנף) are "bull", "serpent", and "wing" in Hebrew.
- The Yamai sisters appear in the Date a Live OVA as a cameo at the arcade which Tohka and Shido are at.
- Any word Yuzuru starts her speeches with will always have exactly two kanji in Japanese.
- Kaguya loves cool things and hates studying. Yuzuru loves junk food and hates loud noises. 
- Raphael was decided on having a wind attribute early on, but the Angel's form was not always a bow, with some ideas including a centaur or a chariot. The Yamai sisters' Astral Dresses also had concepts like "bandit" or "sylph" before "bondage" was settled on.