Kaguya and Yuzuru both appear in this world around the Pacific Ocean. However, their arrival creates a cyclone that pushed them near the shore of Arubi Island, causing a violent storm to occur in that area. After descending on the ground, Kaguya declares to Yuzuru that after a battle record of 25 victories, 25 loses and 49 draws, her magical eye has already predicted her victory, to which Yuzuru makes fun of Kaguya, saying that there are no examples of Kaguya’s magical eye hitting its prediction. As they prepare to once again clash, their battle is paused by Shido who yells for them to stop. Seeing Shido’s presence, Kaguya suggests an alternative contest by using a third person to judge. She proposes that the last contest be to see the one who can seduce Shido. Agreeing to these conditions, Yuzuru accepts the challenge and states that she will win because she is the more charming one.
As they follow Shido back to the museum, where all other students are taking shelter, Shido tells them to change their Astral Dresses to match the summer uniform from his school. Afterwards, Reine creates a cover story from them by telling the rest of the class that they are exchange students that will transfer in next semester, but decided to join earlier for the trip. As the two continue their antics to seduce Shido, they inform him that there was only once an original Yamai, but that person split into the two of them after traveling into this world multiple times. The personality of the original is gone, so one of them must become the new main personality for Yamai. They will use Shido to decide which one of them is worthy of becoming the new Yamai. Following this, the two sisters leave to talk to Reine, who informs them that she can help them win Shido over.
The two then decide to change the signs for the public bath, tricking Shido into entering the girl’s side. Then, the two continue their antics at trying to seduce him. However, their antics only result in another fight between the two them, with Yuzuru making fun of Kaguya’s scrawny body, while Kaguya returns the insult by calling Yuzuru overweight. However, the conversation soon ends, as Shido finds Tohka jumping into the bath, After revealing their deception, Shido struggles to escape before Origami and the others start to enter the bath.
After the bath, Reine decides to put Kaguya in Tohka’s room and Yuzuru in Origami’s room. As Kaguya eats the Pokey given to her by Ai Mai and Mii, she starts a conversation with Tohka, who is impressed by all the difficult words that Kaguya knows. After remembering that Tohka was the girl that Shido was carrying on his back, she inquires to know more about him from Tohka. Meanwhile, Yuzuru also seeks advice from her new roommates at winning over the other gender, to which Origami begins to give a reply. After Shido returns to his room, both Kaguya and Yuzuru sneak in while wearing yukatas. As they continue their seduction tactics, Shido becomes flustered and flees from his room in embarrassment.
During the next day, the group goes to the beach in their swimsuits. They then request Shido to put sunblock on their bodies. Afterwards, Reine arranges for a volleyball game, with Shido, Kaguya, and Yuzuru on one team against Tohka, Origami, and herself. Despite initially losing, they are able to turn the tide as soon as they start cooperating together. After the battle, Kaguya requests to talk to Shido in private. When Shido asks why she talks the way she does, she replies that it is necessary for a Spirit with a super and tragic backstory. Then, tells him that she should choose Yuzuru as the person who lives, citing how Yuzuru was the cuter one. Despite not wanting to disappear, she wants Yuzuru to live on more. Before she leaves, she threatens to Shido to blow away the island if he does not choose Yuzuru. A few minutes later, Yuzuru appears before Shido and requests that he chooses Kaguya, since she has a more charming personality. Similar to her sister, she threatens misfortune to Shido’s friends if he does not choose Kaguya.
Later that night, as Shido is discussing to Tohka about the situation between Kaguya and Yuzuru, both of them overhear the conversation. Angry that the other one is choosing to sacrifice themselves, they both agree that the only way to settle the matter is with a battle. Assuming their Astral Dresses and Angel, both of them take to the sky and start fighting again. However, the fight is interrupted by Shido and Tohka, after the later used his Sandalphon to split the sky in two. He tells both of them that he can offer a third choice: both of them living together in exchange for their Spirit powers. As the two imagine what it would be like to go the school together, they both start crying, with both saying that they want to live with each other. However, the moment is interrupted by the <Arbatel> ship that had sent an army of <Bandersnatch> units to capture them. However, the two easily counter by combining their Angels together to reveal its true form: <Raphael El Kanaph>. Their true Angel takes the form of a bow, which they use to shoot an arrow that destroys all the <Bandersnatch> units and pierces through the <Arbatel>, destroying it.
Afterwards, they both descend on the ground and thank Shido for his help. They then both kiss him at the same time. However, much to their surprise, their Astral Dresses start to disappear. As Tohka appears, Kaguya tells her that Shido suddenly stripped them of their clothes, and Yuzuru bemoans that she can’t be a bride anymore. The next day, the Yamai sisters appear and declare Shido to be their shared possession. They then join Origami and Tohka in clinging onto Shido.
After being sealed, the Yamai sisters transfer into the class next door to Shido, as their mental states are stable as long as they are together. Later, the Yamai sisters are in school, listening to Ai's conference on the Tenou Festival. They seem to fit quite well in human society, getting along well with each other. Maybe too well, as Shido thought to himself. When Origami fights with Tohka over Shido, Kaguya and Yuzuru join in as well, claiming that Shido is their shared property. This fight makes Tonomachi and the other male students to nominate Shido as the Tenou Festival executive member. During the day of the Festival, Kaguya and Yuzuru, while dressed as maids, spot Shido dressed as Shiori and tease him about his cuteness.
They are later shown attracting people to the Maid Cafe alongside Tohka. Later, when Shido's group is going to perform without having enough members, Kaguya and Yuzuru arrive to help him, saying that they heard what happened from Kotori. They know how to play music from their previous music talent competitions. Kaguya is good with the drums, while Yuzuru knows how to play the bass. As a result, they can fill in for the remaining positions Shido needed for their band to preform.
Moments before they have to perform, the twins and Tohka are not too nervous despite Shido himself feeling anxious. The Yamai sisters even praise Tohka for having to play the tambourine. During their performance, the audio track they prepared for lip syncing is damaged by the battle occurring outside between the DEM Wizards and Origami. Luckily, Tohka is revealed to have a fantastic singing voice, enough for them to continue their song without much trouble. When the Festival results are announced, Kaguya and Yuzuru say that, since they helped, it was obvious they would win. When Miku gets angry at losing, she decides to summon <Gabriel>, and the Angel's power is enough to brainwash both Kaguya and Yuzuru, forcing them to attack Shido and Tohka.
Kaguya, Yuzuru and Yoshino are still controlled by Miku, and they offer her drinks and massages to calm her down. Kaguya gets upset when Miku praises Yuzuru's drink, but then Miku apologizes to Kaguya, saying that she feels like she is in heaven.
Later, when Miku sees Kurumi helping Shido, she gets angry and tells Kaguya and Yuzuru to go with her back to the stage. Once Shido and Kurumi approach Miku, Kaguya and Yuzuru use <Raphael>'s powers to defend Miku. When Kurumi sends Shido towards Miku with a clone, the Yamai sisters are unable to help due to being overrun by the clones. When Shido and Miku get out of Kurumi's shadow, Miku has the Yamai sisters chase after Shido and Kurumi, only to be slowed down by <Zaphkiel>'s Second Bullet, <Bet>.
After that, Miku is upset about the things Shido told her, and Kaguya and Yuzuru try to cheer her up by telling her to not think about him. When Miku asks the others what they think about Shido rescuing Tohka, the Yamai twins and Yoshino claim that Shido would even risk his life to save her.
The twins appear once again outside the DEM building when Miku decides to assist Shido in rescuing Tohka. Even though Shido call out to them, the sisters and Yoshino don't listen to him. While Mana is fighting Jessica, Yoshino, Kaguya and Yuzuru try to fight her, but they just end up saying that she is more powerful than the other Wizards, so they start attacking the AST instead. Soon after, when Origami appears with the SSS CR-Unit, she is surprised to know that Kaguya and Yuzuru are Spirits. Even so, the Yamai sisters threaten to kill Origami if she goes against Miku.
After Miku loses her hold on the Spirits, Kaguya and Yuzuru help Yoshino deal with the attacking Wizards, but are later attacked by Origami. Kaguya uses her powers to strike her down, but Yuzuru goes to help and asks her what is happening. Upon being told that Shido is indanger and passing out, Yuzuru then leaves Origami with the other AST members.
When Inverse Tohka attacks Shido, Kaguya and Yuzuru intercept and save him from her attack at the last moment. After saying that this wasn't hard for them to accomplish, the twins throw Shido towards Tohka so that he can save her. Once that incident is over, Shido passes by the Maid Cafe in order to visit Miku, only to get teased by Kaguya and Yuzuru for not being dressed as Shiori.
The Yamai sisters, along with the other Spirits, see Miku clinging on to Shido. The twins scold Miku for her actions and declare Shido to be their shared property. As Miku apologizes to Yoshino and the twins over what she did, Miku tells the Spirits that she was about to give Shido a good-bye kiss. Miku then says that they should all share that kiss, scaring the other Spirits as they run away from Miku.
After arriving late to school, Shido is confronted by the Yamai sisters, who are wearing their gym clothes. Due to Natsumi’s pranks, the two chase after Shido, while wearing their school swimsuits. They demand that Shido give back the clothes he stole from them, as well as Yuzuru wanting revenge for drenching her clothes with water. They proceed to chase after Shido, who runs away confused over what is happening.
After finding out that Natsumi had transformed into one of his friends, the Spirit told Shido that every day someone would disappear if he could not find her. As a result, Shido begins to have a date with every suspect in each of the photos that Natsumi gave him. The last date during the first day is with Yuzuru. Yuzuru scolds Shido for being late, to which he apologizes. Shido then notices that Kaguya isn’t here, which he feels odd since the two are always together. Yuzuru asks if she alone isn’t enough, to which Shido denies, but adds that it was rare to see them apart. Yuzuru tells Shido that she and Kaguya share one mind and body, but she will be the one hogging Shido today. As they go for a walk, Yuzuru asks Shido which one of the twins he likes more. As Shido struggles to give an answer, Yuzuru scolds him for being indecisive. Shido asks her which one she wants to choose. Yuzuru replies that if she chooses Kaguya, she would praise Shido, but she would be both happy and angry if he chooses her. Yuzuru tells Shido that she and Kaguya share likes and distastes, so Kaguya also cares a great deal for Shido. Feeling that she has said too much, Yuzuru runs away while telling Shido to take care of Kaguya.
The next day, Kaguya runs into Shido’s house, telling him that she hasn’t seen Yuzuru since yesterday. In order to calm Kaguya down, <Fraxinus> lies to Kaguya by telling her that Yuzuru has gone for an inspection. For Shido’s date with Kaguya, the two of them go bowling. However, during the date, Kaguya requests a match, in which the loser has to fill out one request for the winner. After Kaguya wins, she tells Shido that for the next ten minutes he has to vow that he will not be surprised with what she does, and also he must swear that to never tell anyone what happens during that time. As Shido agrees, Kaguya lies down on Shido’s lap, and starts crying, telling Shido that she knows they can’t find Yuzuru, and begs for Shido to find her sister.
During the last day, Kaguya is among the final suspects. As Natsumi’s mirror appears in front of them, telling her that each one of them will start to disappear every 10 minutes if they can’t figure out who she is. Kotori and Origami suggest that Yuzuru was the imposter, since she was the first person to disappear. Hearing this causes Kaguya to distort her face in displeasure, as she felt that they were accusing her sister of being the criminal. However, declaring Yuzuru as the culprit causes Origami to disappear. Angered by Natsumi’s actions, Kaguya yells for Natsumi to give her sister and friends back. As she tries to punch the mirror, she is easily blown back. Kotori tells Kaguya that her current Reiryoku levels make her unable to do anything to Natsumi. After Kotori hastily declares Tohka to be the suspect, Kaguya is the next person to disappear.
However, after Shido figures out that Natsumi had transformed into Yoshinon, Natsumi’s mirror releases all of her captives, including both Kaguya and Yuzuru. However, angered that Shido had seen her true form for a second time, Natsumi uses her <Haniel> to transform everyone into children before flying away.
The Yamai twins are among the Spirits that got turned into children by Natsumi. While the other girls are bothering Shido, Kaguya and Yuzuru are trying to steal Kotori's Chupa Chups. When Reine arrives to help Shido, she has Kaguya and Yuzuru apologize to Kotori, claiming that they wouldn't like it if someone else ate their candy. The sisters sleep in Kotori's room afterwards. When Shido goes to school, Tohka, Origami and the Yamai sisters enter the classroom, causing some misunderstandings which cause them to call Shido a "lolicon". When Natsumi causes further trouble for them, they leave the school.
Soon after that, Natsumi uses <Haniel> to turn the Itsuka residence into a zoo, with every girl dressed like an animal (Kaguya being a monkey). Later, they help during Natsumi's fight with Ellen. Once she is wounded by the Wizard, the Spirits transform back to normal. When Shido is trying to convince Natsumi that she can be beautiful without her powers, Kaguya and Yuzuru take care of her hair. They reveal then that Yuzuru won the 71st competition, the shampoo battle, while Kaguya won the 72nd contest, the hair caring contest.
Later on, when the Spirits are deciding Natsumi's clothes, Kaguya suggests a gothic outfit. When Natsumi tries to escape the Ratatoskr underground facility disguised as Kotori, she tries to convince the Yamai twins and Miku that she is ugly, and evil, but they remind her about the things Shido went through to save them.
Afterwards, the Yamai twins help the Spirits trying to destroy the DEM artificial satellite, using their powers of wind to try to delay the descent of the satellite. However, they are attacked by a <Bandersnatch> unit while doing it. Thanks to Natsumi coming to their aid, they only end up with some light injuries. Kaguya and Yuzuru both agree to be Natsumi's friends. When Shido finally seals Natsumi's powers, the Yamai sisters, along with the other Spirits, mock Shido for being so daring.
When Shido meets with Tohka to go to school together, she tells him that Kaguya and Yuzuru went ahead on a competition on who would reach the school first. After Origami kidnaps Shido, Tohka and the Yamai Sisters return to the Spirits mansion, joking about Shido being weak. The twins are the only ones that suspect it's strange for him not to appear this late.
Once they arrive at the mansion, a funny scene ensues when Miku tries to hug the three of them, but they both dodge her. However, while the four girls discuss Shido and Origami's absence, the spacequake alarm sounds. The girls try to go to the nearest shelter, but they are stopped by Origami. Once she attacks the Spirits with a new CR-Unit, Kaguya and Yuzuru are the first to manifest their limited Astral Dresses and Angel to stop Origami, but she uses her Territory to obstruct the sisters’ movements.
Miku uses Gabriel to restrain Origami, while Tohka, Kaguya and Yuzuru charge at her with their Angels. However, Origami used a super dense Territory to blow away Gabriel's pipes and paralyze Tohka and the Yamai sisters. Later, Tohka wakes up to find Kaguya collapsed on the floor. Origami held Yuzuru by the neck and preparing to pierce her stomach with her sword. However, Kaguya gets angry at this and manages to break Origami's CR-Unit with her lance.
Furious at Kaguya, Origami activates her Territory again to overwhelm them, forcing Tohka to be close to inversing again. Just as Origami is about to stab Yuzuru, Tohka manifests her full Astral Dress. After Tohka blows Origami away with Sandalphon, as she confirms that Kaguya, Yuzuru and Miku are safe. When Kaguya sees her Astral Dress, she praises Tohka and asks her to teach her how to manifest it. Yuzuru, however, asks if Origami is alright, to which Tohka replies to she is not dead at least. When Tohka checks up on Miku, she imitates the Yamai sisters’ voices to get a kiss from Tohka, but the twins warn her about it and get angry afterwards. When Origami appears in the sky as a Spirit, the four girls are surprised. Kaguya and Yuzuru carry Miku by her shoulders so as to not hinder Tohka. After Shido interrupts Tohka and Origami's fight, all the Spirits, including Kaguya and Yuzuru, are sent to the hospital to treat their wounds.
Yoshino wipes Kaguya's face with a wet cloth, and she acts tough, even though tears begin to form in the corners of her eyes. Yuzuru teases her about that. When Shido asks about Origami, the Yamai twins comment on how powerful she looked. Later, they spy on Shido when he tries to seal Tohka's powers. Afterwards, they tease him for feeding Tohka.
When Inverse Origami appears, Kaguya and Yuzuru, along with the other girls, gasp in terror. However, they soon agree to lend their strength so that Shido may approach her. The Yamai twins use their powers to lift Shido up when he decides to face Origami. While flying, the sisters treat Shido like a child, saying that he flies skillfully. When Ellen confronts them, Kaguya charges at her, giving Yuzuru the chance to throw Shido towards Origami, only for him to find that she is beyond salvation now.
Kaguya and Yuzuru first appear in the New Timeline, when Shido and Tohka are about to go to school. Kaguya thinks Shido was staring at their chests, to which Yuzuru replies that it's only a natural reflex for males. After Kaguya forgives Shido, Yuzuru teases her about having a diary with indecent delusions of Shido. They both run off to school soon after that. While Shido is dating Origami, the Yamai sisters are playing video games at the Spirits’ mansion. Suddenly, they feel something had happened. Soon after, they use their powers to save Fraxinus from Inverse Origami. When Shido states that he wants to save Origami, the Yamai sisters agree to help him from the skies by providing a distraction for Demon King <Satan>’s attacks.
Once Origami is sealed, the twins wait for her to arrive in the classroom. Kaguya still holds a grudge against her for what happened in the Old Timeline. Meanwhile, Yuzuru is just happy that Origami changed her view on Spirits. They retreat to their classroom once they greet Origami good morning.
As Shido and Tohka make their way to school, Kaguya and Yuzuru show up and tease Shido for holding Tohka’s scarf by comparing it to clutching onto the leash of a dog. The duo then run away to school, with Shido and Tohka in pursuit of them. After arriving at the front entrance, they inform Shido it was just a joke, though Yuzuru also adds that it was because Kaguya was jealous. During the physical examination, the Yamai sisters decide to compete with each other by seeing who can come closest to a set value. Like everyone else, they are stunned when Shido suddenly collapses.
As the Spirits wait in the underground <Ratatoskr> facility to hear Shido’s condition, the Yamai Sisters scold Natsumi for her negative thought process on the grounds that Tohka might believe it. As Reine arrives and explains the situation, she tells everyone that they need to kiss Shido in order to restore the Path to normal. As Tohka asks if everyone else had kissed Shido before, Kaguya asks Tohka how she thought Shido sealed away their powers. However, before they could proceed, Shido has disappeared from his hospital bed.
After finally finding Shido, they are shocked by how he was using everyone’s power, but even more so by the new flirtatious personality he had. As Kotori gave the Yamai Sisters the command to physically restrain Shido, he easily avoids them by using Natsumi’s powers to transform every present into Shiori. The Yamai Sisters and the others are then issued a challenge by Shido, to make him fall for everyone on a date. Back at the base, both comment on how Shido's personality has changed drastically. It was almost as if he had become a Casanova. Reine remarks that the combination of his cold and the overheat must have caused him to experience an euphoric high of sorts. Reine then arranges a plan where each Spirit would have a 45-minute date with Shido. Additionally, she warns everyone against using their powers, as there is a time limit on usage because the current situation prevents a counter flow of Reiryoku circulating between them and Shido. After the plan is done, they invite Shido to a warehouse where they are all wearing swimsuits. During the Yamai Sisters' date with Shido, the work together to seduce Shido through a combination of their swimsuits and eating ice cream.
During the final battle to save Shido, the Yamai Sisters quickly assume their Limited Astral Dresses, to which Kotori scolds them since they could only use their powers for five minutes, and they can't waste any time using them for a strong bravado. As they glide through the sky, both summon their Angels. Kaguya's lance breaks through the barrier surrounding Shido, allowing Yuzuru to restrict Shido’s movements by using her chains. Immobilizing Shido, both kiss him at the same time, telling him to come back to his senses.
After Shido is saved, the Yamai Sisters are among the group who walk in on Tohka kissing Shido. While Kaguya praises Tohka for being so bold, Yuzuru responds that Kaguya is secretly jealous.
As Shido discusses, the situation with Nia to Kotori, Kaguya’s voice can be heard asking Shido to offer a sacrifice of food to her stomach. Then, Yuzuru tells Shido that Kaguya wants to eat some of his delicious food, which causes Kaguya to yell at Yuzuru for twisting her words. After Shido reveals that Kotori use to wet the bed, she lets out a scream from the kitchen. Hearing the loud noise, the sisters ask what happen. However, Kotori quickly changes the topic and tells them that it was about wetting the table. Despite not completely believing it, the two relent and follow Kotori’s orders to set the table for dinner.
After the failure of the visual novel plan, Kotori recruits the other Spirits to help create a plan for wining Nia over. Here, Kaguya voices her surprise that Honjou Souji was actually a woman. When Shido asks Kaguya if she reads manga, Yuzuru responds that Kaguya secretly buys Ecchi manga by inserting it between battle manga and sport manga. Then, Kaguya retaliates by saying that the Shoujo manga that Yuzuru always reads have even more explicit scenes. As Yuzuru asks in what regard, Kaguya embarrassingly struggles to come with an answer. However, their discussion is stopped by Kotori, who tells them to save it for later.
After Origami comes up with the plan to draw a manga based on Shido’s past experiences with the other Spirits, Yuzuru states that it’s a good idea, which is to be expected from Master Origami. They tell Shido that they have prior experience drawing manga, during their 39th match; they tied again, during their illustration submission showdown. Both of their works got printed together under the title [Rare illustrations from twins!]. However, before they can start, the conversation is interrupted by Nia, who had hacked into <Ratatoskr>’s communications system by using her Angel. The Yamai sisters both comment on how angry Nia looked. After Kotori made the sales challenge to Nia at Comico, all the Spirits started drawing an illustration of Shido to see who would be the main artist.
Kaguya’s drawing depicted Shido in a hot-blooded Shōnen style. Meanwhile, Yuzuru’s drawing depicted a bishonen Shido drawn in Shōjo style. Both illustrations were drawn very well, so Kotori added them as candidates for the artist position. As Origami presents her drawing, Kotori shrieks upon seeing the inappropriate content. However, both Yuzuru and Miku intensely stare at the picture being drawn. Eventually, it was decided that Natsumi would be the main artist, and that the Yamai Sisters, Origami, and Shido will be the supporting artist. For the next two days the Yamai sisters worked tirelessly on the doujin.
During the process, the Yamai Sisters helped with erasing the pencil traces and inking the image before sending it to be scanned into data. During the work process, the Yamai Sisters insisted that Natsumi get some rest, however the younger Spirit refused on the grounds of wanting to try her best to help everyone. After finally finishing their work, both sisters collapsed in exhaustion. During the sales challenge at Comico, they helped sell the doujin by organizing the line. After they tie with Nia in sales, the Yamai Sisters were among the ones overjoyed when Nia said that she would give Shido a second chance.
However, their joy was short lived, as Nia started inversing due to Westcott’s actions. Upon Ellen arrival, the Yamai Sisters and Miku assist Tohka in distracting Ellen. However, after Westcott absorbed Nia’s Qlipha Crystal, their group returns to Shido’s side, having sensed that something went wrong. Like everyone else, they were terrified that Westcott gained the ability to use <Beelzebub>. After Nia recovered from her emergency surgery, Shido takes everyone out to see the first sunrise of the New Year. Like everyone else present, the Yamai Sisters both express their shock when Nia states that every Spirit use to be human.
Three days after the New Year, the Yamai Sisters join Shido, Tohka, and Origami in praying next to the shrine. After finishing, Shido asks them what they wished for. As Kaguya gives off an overly bombastic introduction, Yuzuru quickly retorts that Kaguya wished for wanting to climb up the stairs of adolescences this year. Criticizing her twin for saying that in an overly serious tone, Kaguya states that she obviously wished for a date with Shido. After realizing what she said, the now embarrassed Kaguya starts hitting Yuzuru's back in frustration. After hearing Origami's wish, Kaguya's cheeks flushed with a red color and quickly rushed over to prevent Tohka from hearing it, saying it was to early for the more innocent Spirit. Afterwards, the Yamai sisters follow the others in hanging up their own wishing plaques.
Much later, the Yamai sisters and the other Spirits fall down from their hiding spot, revealing that they had all been eavesdropping on Shido's conversation with Mukuro. As Yuzuru struggles to get up, she complains that Kaguya needs to lose weight, much to her twin's agitation for being singled out. After everyone agrees to lend their strength to Shido, Yuzuru questions Reine if there is a way to unlock Mukuro's heart. Reine responds that since Mukuro's <Michael> was responsible for sealing away her emotions, using it again would likely unlock her emotions. Kaguya then boldly declares that she will use force to make Mukuro open her heart again. In return, Yuzuru expresses her doubt, as they have no means to travel to Mukuro's location. Hearing this, Kotori quickly remembers something and decides to take everyone into a secret Ratatoskr base where the new Fraxinus EX is being built. The Yamai sisters and the others are then marveled by the presence of the Fraxinus EX's AI, MARIA, which can now communicate directly to the crew. Then, MARIA informs everyone that Ratatoskr's founder, Elliot Woodman, would like to have a word with them.
After Woodman explains his reasons for leaving DEM and creating Ratatoskr, he introduces everyone to Karen, who had also left DEM with him. Much to everyone's shock, Karen announces that she is Ellen's younger sister. However, the peaceful conversation is interrupted by DEM, who had found their location from <Beelzebub> and has begun their attack. As they make there way for the Fraxinus EX, the Yamai sisters and the others accidentally run into Westcott in the process. Despite their best efforts to resist, Westcott uses <Beelzebub>'s ability <Ashufiriya> to transport everyone into a world of fantasy as they are all swallowed into the respective books that emerge beneath their feet.
In the fantasy world, the Yamai Sisters stumble upon Kotori, as she was slowly starting to freeze to death. In an attempt to wake her up, they pretend that Shido is groping her, causing her to wake up in embarrassment. However, Kotori is still to weak from the cold, so they all decide to warm up using Kotori's matches. However, upon creating a fire, the flames invoke illusory images of food and Shido, much to the twins' shock. Kotori notes that the power of the matches must have to do with her appearance being similar to The Little Match Girl, and briefly summarizes the fairy tale for the Yamai sisters. As their stomachs start to rumble, Kaguya tells Yuzuru to grab the basket that contained cakes and other sugary pastries. As Kotori questions where did they get such treats, Kaguya explains that they woke up in the middle of a black forest and encountered a house made of candy. Upon hearing their story and seeing the twins' appearance, Kotori summarizes that their story must be based on Hansel and Gretel.
However, Yuzuru notes that they soon fled from the witch that invited them in. After refusing, the witch was enraged and started to chase after them. Yuzuru adds that while running away, Kaguya was crying the entire time, much to the latter's denial. Afterwards, Kotori thanks the twins for saving them. As they question on their next course of action, Kotori tells them that their current plan should be to rendezvous with everyone else first before we come up with a strategy to escape from this world. As they are discussing, a merchant passes by and talks about a mermaid, that keeps singing Darling, being brought to the royal palace, raising. After a few minutes of staring at each other with deadpan faces, Yuzuru notes that this mermaid sounds familiar.
The Yamai twins and Kotori are reunited with Shido's group at the main entrance to the palace. They explain to Shido the mermaid situation and how the guard will not let them inside. As they discuss methods of entry, the twins debate either to sneak in or to knock the guard unconscious, which causes the guard to become even angrier. Eventually, Natsumi appears, having her looks transformed by a magician, and easily gains entrance to the palace. Seeing this cause Kaguya to pout, and she questions the guard why Natsumi gets preferential treatment. Nevertheless, Natsumi's transformation dispels at the strike of midnight, and they are once again rejected entry. Eventually, they decide to use Kotori's matches to create illusions of beautiful dresses, which gave them the appearance of nobles and allowed them to sneak into the party.
After entering the ballroom, Kotori tells everyone to stay within the reach of the torch's light, as leaving it would dispel the illusion. Despite this, the Yamai sisters charged out of the flame's limited range, causing their beautiful dresses to instantly reverted back to the ragged patchy clothing that their representative story characters had worn. The two let out unusual yells of bewilderment and speedily swayed their bodies like trained gymnasts, coordinately leaping backwards into the range of the Kotori's matches. Kotori scolds them for not being careful, to which they apologize and tell her that they will be more cautious.
In the palace, they found Miku as the mermaid entertainment. As conflict arose with the palace guards, the twins prepare a fighting posture, prepared to open a blood path for the others to rescue Miku. However, they are stopped by Origami's timely arrival, who everyone discovers is the king of the castle. Much to the Yamai sisters' shock, Origami did not wear any clothes, since her story was based on The Emperor's New Clothes. After finding everyone, they start brainstorming again for ideas of how to escape from the fantasy world. However, at that moment, the castle is suddenly invaded by the villains from each of their respective stories. For the twins, the forest witch reappears before them and threatens to devour them whole.
Since they could not use their angels in the fantasy world, the Yamai sisters and the others are helpless against the ensuing onslaught. Luckily, they are saved by the appearance of a second Shido, who Natsumi notes must be based on the manga that everyone wrote to impress Nia. After the other Shido manages to defeat all of the villains, he opens a gateway from them with his <Sandalphon>. After returning to their world, they all board the new Fraxinus EX and launch off into space in order to begin the mission to save Mukuro.
The Yamai Sisters and the other Spirits, with the exception of Origami, Tohka, and Natsumi, decide to stay on the Fraxinus EX in order to help with the battle against Ellen. At first, they offered to leave and take care of the other warships that DEM sent along with <Goetia>. However, Kotori asks them to stay on stand by, as the Spirits would be their secret trump card against Ellen. Using the newly installed System Blót within Fraxinus EX, the Yamai Sisters combine their powers with Kotori, Yoshino and Miku to unleash a devastating eruption of energy from the magic cannon that devastates <Goetia>, forcing Ellen to retreat back to Earth. Proclaiming their victory, the twins announce in unison that they are invincible when they are all working together.
The Yamai Sisters are later among the Spirits crowding Shido's hospital bed after he recovered enough from atmospheric reentry.