|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.|
While shopping for items for the Spirit’s dinner, Shido found Nia collapsed on the street from overwork and hunger. Wondering what to do, Shido agrees to help her back to home. Throughout the way back, she uses a lot of dirty jokes and flirty provocation to fluster Shido, much to his discomfort. After arriving at Nia’s apartment, she requests, in an exhausted tone, for Shido to cook something for her. Reluctantly, Shido decides to use some of the supplies he bought to cook a rice soup dish that eventually helps Nia regain some of her energy. Afterwards, she convinces Shido into helping her with erasing and inking of her manga script. 
Just as Shido was about to leave, Nia reveals to a shocked Shido that she knows about his goal to make the Spirits fall for him. In an amused tone, she tells him that she is a Spirit that had been captured by DEM and how she can acquire any information that she wanted to look for. While using her Angel, she explains to Shido that Ellen was able to defeat her through an unexpected ambush, since she has to be actively thinking about the topic in order to use <Rasiel>. Feeling that Shido is underestimating <Rasiel>’s power, she shows him its ability to alter the future for a small increment of time. Nia also reveals to him that she had used <Rasiel> to learn about him and set up their meeting as she was grateful to him for shooting down the DEM plane that was escorting her. As a way of thanking Shido, she agrees to go on a date with him, with the condition that it is in Akihabara.
During the date, Nia and Shido travel to a cosplay store where she wears a nurse costume as a fan service reward for Shido. Comically, she didn't wear it properly in order to further tease Shido. Afterwards, they goes to a manga bookstore where she buys all of her favorite manga volumes that she had missed during her captivity in DEM. However, even though the date is progressing smoothly, Nia’s affection level still remained constant. It was then that she announces her inability to love anything else other than 2D. As a result, Kotori gives Shido the command to cosplay as Nia’s favorite character, Tokiya. While at first amazed that her favorite character had entered the 3D world, she sees through the ruse after seeing Shido act out of character for Tokiya. Eventually, she is angered by his actions and kicks him away.
After returning to her apartment alone, she starts to regret some of her prior actions and remarks that she should have behaved better since she is older than him. However, she also comments that even if she let him kiss her; the Spirit power would probably remain unsealed because it would be impossible for her to open her heart to him. Before she could finish her thoughts, she receives a mysterious package containing a game with Shido as a game character, which Ratatoskr intends to use to make her fall for him. While being satisfied with the game, she decides to use <Rasiel> to search for other works that the company had made, unintentionally discovering Ratatoskr’s intentions and relighting her anger towards Shido.
As the Spirits make a plan to write Shido’s life into a manga, Nia uses <Rasiel> to hack into Ratatoskr’s connection system. There, she voices her desire that she would not even read their work, partly out of anger towards Shido and partly because of her busy schedule as a manga artist. However, Kotori then decides to challenge her to sales battle at Comico. If they win, she would have to read their work. Unimpressed that they think they can defeat a professional manga artist, she agrees to the challenge.
Afterwards, Nia remarks on why she loves 2D. The omniscient angel, <Rasiel>, made her distrust everyone, since it allowed her to see the dark side of humanity. It told her how people would talk behind her back and lie to her. 2D is her only refuge, her escape from the distrust sowed by reality. The characters there could still be complex, yet they could never betray her. She also made a remark about her past, remembering the time when she used <Rasiel> to answer how she was born as a Spirit. Thinking back, she blithely remarks that she would have been a more sensible Spirit if she had not used <Rasiel> at that time.
As she is lost in her thoughts, debating whether or not to use <Raisel>, Nia is approached by Kurumi. She quickly uses <Rasiel> to scan Kurumi’s background and discovers that Kurumi was the reason that the transport plane lacked an escort. Knowing that her powers would be unable to defeat her, she decides to approach the situation cautiously. Although Kurumi is able to collect information easily through her clones, <Rasiel> still had some secrets that she didn’t know, while Nia already knew all of Kurumi's abilities. However, Kurumi responds that she wasn’t here to be her enemy and is only here to inquire information about the First Spirit, much to Nia’s shock.
As the sales battle began, Nia and Shido exchange pleasantries, and as custom dictated, traded each other’s works. However, Nia states that she wouldn’t even consider reading it unless they somehow managed to beat her. As the battle begins, Nia has the advantage, since her name as pro attracted a great deal of fans. However, Ratatoskr’s side manages to have a comeback by dressing the Spirits in bunny outfits to promote their work. During the contest, Nia is approached by her old friend Takajou, who tells her that no matter what happened, she will still remain a fan of Nia's works. As Nia struggles to give an answer, Takajou says that she has probably overstayed her welcome and leaves. Noticing this, Shido asks Nia if she is afraid that she will eventually lose to her curiosity and eventually find information from her Angel that would push her friends away. Angered by this, Nia yells that Shido would never understand what it feels to have a power that makes privacy worthless. The two start to quarrel as they continue selling books, with Shido saying that he won't hate her if she uses <Rasiel> on him. Nia frustratingly replies back that she would likely be the one to hate him if she investigates about him.
Eventually, the battle ends in a tie and Nia agrees to read their work after accepting defeat. While initially unimpressed, she is curious on how they managed to complete the work within only two days. As she uses <Rasiel> to find out the reason, she sees how each Spirit started out distrustful like her, but still gradually got immersed in Shido’s light and found acceptance in the world through him. The Spirits' story about how they changed themselves after meeting Shido brought Nia to tears. She decides that she would give Shido a second chance date. However, at that moment, Westcott releases the Realizer he had installed in Nia’s brain, forcing her to remember all the torture she endured when she was captured by DEM. Unable to handle the shift from hope to despair, Nia begins to inverse.
Soon after, Nia is unable to control her actions and summons her Demon King, <Beelzebub>, to unleash a swarm of shadow creatures from it’s scattered pages. While the Yamai sisters, Miku and Tohka are busy fighting Ellen, Nia uses <Beelzebub>’s ability to manipulate the future to redirect Natsumi, Origami, and Yoshino’s Angels against their owners. As everyone became restrained, Shido awakens the powers that he had started getting a feeling for by remembering the time he went berserk during the beginning of the month. He attempts to awaken Nia’s consciousness by using <Gabriel>'s ability. While it seemed to have an effect, Artemisia emerges from the shadows and stabs Nia with her sword. She is also able to use her Territory to extract Nia’s Qlipha Crystal through unknown means. The crystal is then absorbed into Westcott, who steals Nia’s ability to use <Beelzebub>.
Westcott, however, decides to retreat after he has Nia's Qlipha in possession, as he wants to have the fun for later. The crystal extraction leaves Nia at the brink of death. But fortunately, Tohka notices that Nia still had some Spirit powers left. Kotori notes that it was because the extraction wasn’t complete, as Shido was able to awaken some of her consciousness beforehand. It is then that Shido decides to seal Nia, hoping that the cycle of Spirit Power between him and the other Spirits would heal her. The endeavor is a success, and Nia slowly thanks Shido before closing her eyes again.
Afterwards, Nia undergoes a treatment using a medical Realizer in order to stabilize her condition. Even though she was already awake, she is still recovering and has to remain in a wheelchair. Shido decides to take everyone outside in order to see the first sunrise of the New Year. During the ensuing conversation, Nia reveals that she had been a Spirit for almost 30 years and questions when the other Spirits became one as well. Kotori tells her about when she became a Spirit, along with Miku and Origami, but adds that the rest are pure Spirits. Nia then responds in a questioning tone by saying that every Spirit use to be human, shocking everyone present..
Seeing everyone's shocked expressions following her statement that all Spirits use to be human, Nia quickly dismisses it as a joke. However, later she has a private conversation with Shido and Kotori, where she told them what of she knows. The group is then joined by Origami and Mana, who both arrive. The former found the meeting to be suspicious, while the latter wanted to talk to Shido. However, Nia gets distracted when she hears Mana call Shido "Nii-sama", causing her to make fun of Shido by calling him a siscon. Nia also upsets Mana by calling her Imouto #2, giving her the number 2 position despite Mana arguing that she is the blood sister. She then decides to call her Manacchi, which causes Mana to say if Nia is comparing her to a manatee.
After things finally start to calm down, Nia reveals what she knows about Spirits. She says that their definition of a "Pure Spirits" is flawed, since she also originally appeared in the world through spacequakes and had no memories, except for the knowledge of how to use her angel. Using <Rasiel>, she was able to obtain information about her past. Back then, a mysterious person gave her a Sephira Crystal containing <Rasiel> after an incident where she had lost all hope in living. Despite her efforts, she was never able to find out who gave her the crystal, as the information gathered by <Rasiel> was undecipherable to her. Her knowledge causes Shido and Kotori to wonder if everyone else had a similar situation, with Kotori noting that they should search information about a possible lost child 30 years ago. Nia apologizes, as she states that they could have easily found out if she could still use <Rasiel> to search everyone else's past. However, Origami notes that she must still have some spirit power left, since she was able to be sealed by Shido. Origami explains that her powers should be able to flow back when she has a restless consciousness.
Despite being exhausted, Nia gathers her focus and is still able to summon her angel and limited Astral Dress. However, she notes that although <Rasiel>’s ability to scour for information is still functional, it can no longer be transmitted it to her. Similar to her situation with the one who turned her into a Spirit, she can't understand anything that is inscribed here anymore. However, she notes that some information is still readable, learning where Shido hides his secret treasure. She notes that since <Rasiel> and <Beelzebub> use to be the same embodiment, they shouldn't be able to exist simultaneously, <Beelzebub>'s user would be suffering from the same problems. Nia remarks that it would be better if she should be the one who has to get hurt. However, Shido replies that they can't let anyone be injured, causing Nia to blush shyly. Afterwards, Kotori tells everyone to leave the room in order to allow Nia to rest.
Three days later, Nia and the others visit a shrine for the first time in the new year. Along with Natsumi, they both start drawing something on their wishing plaques. Shido notes it looks like two manga artist hastily working before a deadline. Nia states proudly that she can only draw something of this level now because of her condition. As Natsumi starts acting negative again, Nia says that Natsumi has a great future and even wants her to be her own personal assistant. She offers to pay for her a salary and introduce Natsumi to her editor. As Shido tells her about the kimono that <Ratatoskr> had prepared for her, she says that she didn't want to wear one since she finds it difficult to move in them. She then teases Shido by asking if he has a kimono fetish. Then, to further tease Shido, she hands him a illustration for a wishing plaque that Kotori refused to allow her hang up because of its inappropriate content.
Moving back to previous statement, she offers both Natsumi and Shido to work for her. At that moment, Miku arrives and demands to join in as well. However, Nia states that would be difficult because she can't afford a salary for an idol. After Shido falls down on top of Tohka, Nia jokes that the position is almost identical to her illustration, noting that these wishing plaques do have some power to them. She then writes down that he wants "boy" to be her bride, flustering Shido since, even in that case, he should be the groom. Despite trying to be energetic, Nia is eventually forced to sit down because of a headache, with Shido and Kotori telling her to not push herself since she hadn't fully recovered from her near death experience.
After the initial failure to convince Mukuro, Nia and the others suddenly crash out of their hiding spot, revealing that they had been eavesdropping on the entire conversation. Nia remarks that she can't let Mukuro destroy the world because she still wants to read her favorite manga. Everyone soon agrees to once again lend their power to help Shido. However, the question is raised on how they are going to approach Mukuro when she is in space. Kotori quickly remembers something and decides to take everyone into a secret Ratatoskr base where the new Fraxinus EX was being built. Amazed by the sight of the ship, Nia quickly asks if she can take a picture as a reference for her manga, to which Kotori bluntly rejects because the work is classified. Nia 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.
As they were walking, Shido sees that Nia had a complicated expression. Nia tries to pass it off as a joke, but in privately whispers to Shido that she feels like she had heard the name Woodman before. After they arrive in Woodman's study, Nia calls out Woodman on his goal in saving Spirits, asking how a co-founder of DEM could say such words. She tells everyone that she had used her <Raisel> a month ago to discover that Woodman, along with Westcott and Ellen, were responsible for the appearance of the First Spirit 30 years ago. In response to Nia's accusations, Woodman confesses that he once worked with Westcott, but changed his intentions to protecting other Spirits after falling in love with the First Spirit.
At that moment, DEM begins their attack on the Ratatoskr base. Nia bitterly notes that Westcott must have used <Beelzebub> to find their location before she had time to jam his information network. As they make there way for the Fraxinus EX, Nia and the others accidentally run into Westcott in the process. Despite their best efforts, Westcott uses <Beelzebub>'s ability <Ashufiriya> to transport everyone into a world of fantasy. Despite Nia's attempts to use <Rasiel>, she and the others are all swallowed into the respective books that emerge beneath their feet.
After arriving at the fantasy world, Nia and Tohka appear just in time to save Shido and Yoshino from a malicious wolf. Nia suggests that Tohka feeds the wolf one of the dumplings in her bag. After eating, the dumpling, the wolf suddenly becomes complacent and starts to repent for his prior actions. Nia remarks that Momotarou's dumplings are very effective against simple minded creatures like the wolf. After reconvening with Shido and Yoshino, Nia informs them that they have been transported into fantasy world created from the various stories and scenarios that <Beelzebub> has gathered in its database. Being trapped in this world, their appearances have also become intertwined within the stories. While Tohka is dressed as Momotarou, Nia took the appearance of Fatima, the main character from her manga Silver Bullet. Shido remarks that her manga doesn't seem to fit with the fairy tail motif that everyone has. In response, Nia puffs her chest in pride and proudly states that her manga has been rising in the rankings recently and its growing popularity for the public masses has allowed the hands of fate to pick her story.
Shido then starts to worry about the outside world, since they had left just as Ratatoskr was being attacked by DEM. However, Nia assures him that time isn't a huge concern for now, as the flow of time in the fantasy world is slower than the real world. Their primary focus should be to find a prerequisite for escaping this world. As Shido asks for potential escape routes, Nia sarcastically replies that the easiest way would be for Westcott to reopen the passageway with <Beelzebub>. Since that is unlikely to happen, they should search for an all powerful fictional character that has the ability to open the world from the inside. Either way, they also need to search for Kotori and the others, who have also become scattered in this world. Listening to their conversation, the wolf offers to be their guide, as his heightened sense of smell can easily detect outsiders.
Nia and the others reconvene with Kotori and her group at entrance to the king's banquet. Using Kotori's matches to create illusions of beautiful dresses, they were able to sneak into the party. There, they found Miku as the mermaid entertainment, and Origami as the king of the castle. After finding everyone, they start brainstorming again for ideas of how to escape from the fantasy world. Nia suggests that they find a fictional character that has the power to grant wishes, like the magic lamp from Aladdin, or the magic hammer from the One-Inch Boy. However, at that moment, the castle is suddenly invaded by the villains from each of their respective stories. Nia starts to shamelessly advertise the monsters that appear from her manga. Since they couldn't use their angels in the fantasy world, Nia and the others are helpless against the ensuing onslaught. Luckily, they are saved by the appearance of a second Shido, who Nia notes must be based on the manga that everyone wrote to impress her. After the other Shido manages to defeat all of the villains, he opens a gateway with his <Sandalphon>. After returning to their world, Nia and the others board the new Fraxinus EX and launches off into space in order to begin the mission to save Mukuro.
Nia 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. Nia remarks that it resembles a final boss battle where everyone joins forces, but adds that she will only be able to support them from the ship because her Spirit power is still down from her Qlipha Crystal being stolen.
As Shido is relaxing in the bathroom, Nia bursts in after the rest of the Spirits and declares that she is also there to cleanse Shido alongside the rest of the Spirits.
Later, Nia approaches Yoshino and Natsumi, both of whom are watching the spectacle of evacuation due to the spatial quake alarm. Nia quickly explains that there is something happening in Tenguu Tower, and is likely where Tohka, Shido, Mukuro and Origami are.