Rukia Kuchiki vs. Aaroniero Arruruerie

 is Rukia Kuchiki's first battle upon entering Las Noches and is the first battle with a current Espada to take place within Las Noches.

Prelude
Rukia runs up a flight of stairs in Las Noches, but once she reaches the top, she is shocked to see that she's in a room that looks like the outside of the palace, only in the daylight. All of a sudden, someone appears right behind her and asks her if she'd like to know the reason why it appears as if she's outside. When she looks behind her, he disappears, and then reappears directly in front of a tower. The person tells her to follow him, and the two of them enter the tower. The inside of the tower is filled with darkness, and the person states that he doesn't like the sunlight very much. As the person removes his mask, he states that he's Aaroniero Arruruerie, the Noveno Espada. However, after completely removing his mask, his face is shown to be the same as Kaien Shiba, Rukia's old mentor. Rukia is shocked by this and can't believe what she's seeing. She asks Kaien if it's really him, but thinks to herself that it's impossible, as Kaien was killed by her years ago. However, Kaien confirms her question and jumps down from the pillar that he was standing on. He tells her to stop looking at him so weirdly and tells her to be happy since he's alive. However, she begins to cry and Kaien tells her that if she does that he's going to look like the bad guy. Rukia then confirms to herself that this is the real Kaien since the feeling of being around him is the same as it always was. Kaien then begins to look for something and then throws her something to sit on, saying they have a lot to talk about.

Kaien explains to her that the night he was killed his soul flew to Hueco Mundo, since the Hollow that took over his body, Metastacia, was one of Sōsuke Aizen's experiments and would have been equipped with that type of mechanism. Then when the Hollow fused with his spiritual body, it took on his appearance, but his will was somehow strong enough to allow him to have control of that body. Kaien then jokingly states that his "will of steel" was too strong for their calculations. Rukia gets mad at this, stating that this was supposed to be a serious story, but Kaien defends himself by telling her she looks too gloomy. He then continues his story and tells her that he has secretly been working as an Espada to get his revenge against Aizen. He then tells her that the reason there's a blue sky outside this tower is because any place that has light shining on it can be seen by Aizen. Kaien then states that he's glad she was the one who came because he believes that she's the only one who can carry out the strategy he's going to discuss. He tells her that they're changing locations, but as Rukia runs towards him Kaien points his Zanpakutō at her.

Battle
Kaien swings his Zanpakutō at Rukia, but she dodges and he's only able to make a small cut across her cheek. Kaien tells her that she's gotten better at fighting since they last met. Kaien then states that she has a weird look on her face, but then tells her that he's happy that she was able to dodge his attack, since last time she would have been killed. Rukia ignores his statements and asks him how much of what he said was true. Kaien tells her that all of it was true and asks her if she thought that there was anything strange in him trying to kill her, since she was the one who killed him. He then asks her if she's prepared to be killed by him and Rukia tells him that she is, but not right now since while what she did was a terrible thing, she still has to save Orihime Inoue. Kaien tells her that he was just kidding and that he would never kill her over something like that. He then goes back to his original statement that there is something that only she can do, and explains that for her to atone for her sins, she must kill her friends. Rukia is shocked by this, but Kaien tells her not to worry, since she knows all of their abilities and it should be incredibly easy to catch them off guard. As Kaien tells her that her killing him won't be a problem after that, Rukia states that this time he isn't going to say that this is a joke, since this is something incredibly serious. She grabs his hand and tells him not to insult Kaien.

Kaien backs away and Rukia tells him that there's no way someone like him could be Kaien, since he would never tell people to kill their friends and that everyone in the 13th Division knows this. As Kaien tries to convince her that he really is who she remembers, Rukia yells at him not to say Kaien's name again. She then releases her Zanpakutō, Sode no Shirayuki, and Kaien begins to smile at this. A mist is formed around the area and Rukia uses this to sneak attack Kaien. However, he dodges her first blow and appears directly behind her. He then swings his Zanpakutō at her, but Rukia is able to dodge this. Kaien goes after her and swings his Zanpakutō down at her, but this attack is blocked. She then swings her Zanpakutō at him, but Kaien overpowers her and cuts part of her cloak. She falls to the ground and Kaien begins thrusting his Zanpakutō down at her. She rolls away though and successfully dodges the attack. She then blocks his Zanpakutō yet again and moves away. She then swings her own Zanpakutō at him, but she is slowly overpowered and is forced to form a distance between the two of them. She then charges at Kaien and the two clash yet again, forcing Kaien to hide in the mist. He sneak attacks her, but Rukia is able to block his blow. They begin clashing, but Kaien hides in the mist yet again. As Kaien thrusts his Zanpakutō down at her, Rukia decides to use Some no mai, Tsukishiro, but he is able to dodge the huge pillar of ice that forms. After landing on the ground outside of the mist, Kaien explains to her that her two techniques, Some no mai, Tsukishiro, and Tsugi no mai, Hakuren, won't work on him since he knows those moves very well. Kaien then wonders if this is the extent of Rukia's power and decides to release his Zanpakutō, Nejibana. He then tells Rukia that this is going to be the end and warns her to prepare herself.

He swings his Zanpakutō at her and Rukia blocks the blow with her own Zanpakutō. Kaien then swings his Zanpakutō down, conjuring up water and breaking part of the floor that Rukia is standing on. The part of the floor Rukia is on is then sent into the air and Kaien attacks her yet again, only for Rukia to block this blow as well. However, after conjuring up more water, Rukia is overwhelmed and she is forced to form a distance between the two of them. Rukia thinks to herself that everything about Kaien's style of fighting is the same and that no matter how much she tries to deny it, all she can think is that this is really Kaien in front of her. Kaien then swings his Zanpakutō at her, but Rukia blocks this as well. As Rukia resolves to believe in the Kaien in her memories and not the one in front of her, her Zanpakutō is knocked away and Rukia immediately uses Hadō #33. Sōkatsui directly in front of Kaien's face. He dodges the attack though and congratulates Rukia on being able to use a Kidō spell without incantation. However, this attack ends up destroying part of the tower, letting light in, and Kaien jumps out of the way. Rukia is confused by this, as he had the perfect opportunity to finish her off right there. She then remembers back when Kaien decided to come into this tower because of the light outside, and then begins to form a hypothesis. She then decides to test out her theory.

Rukia uses Bakudō #4. Hainawa, holding Kaien down, but he tells her that weak spells like that won't hold him down. However, Rukia uses a double chant and casts Bakudō #61. Rikujōkōrō, holding Kaien down further, and then immediately casts Hadō #63. Sōren Sōkatsui. The Kidō spell hits the wall directly behind Kaien, causing sunlight to enter the tower. Kaien begins to scream in pain, and his true face is revealed to be a glass cylindrical capsule filled with red liquid and two small, floating Hollow heads. Rukia is shocked by this and Kaien decides to reintroduce himself as the Noveno Espada Aaroniero Arruruerie. He tells her that if she's shocked by their faces, then she should just keep it to herself since he got tired of hearing people's opinions on them a long time ago. .

Aaroniero tells her that the Kidō spell she used, Rikujōkōrō, is Captain Byakuya Kuchiki's signature spell and Rukia is shocked that he knows even stuff like that. Aaroniero then states that if she had hit him with that last attack, he would have been heavily wounded, but Rukia explains that killing him is secondary, as knowing whether or not he was Kaien was more important, and that by knowing that she would be able to cut him down without mercy. Aaroniero tells her she's foolish in thinking she could win against him and appears directly behind Rukia. He states that as long as there's shadows, he can always use his powers and goes back into the form of Kaien Shiba. He then complains about the fact that Aizen would decide to make sunlight in a place of total darkness, especially when there are people like him who can only use their powers in darkness. Aaroniero then changes the subject and states that his power is not shape-shifting, and begins to explain that because he's the only Espada who is a Gillian, he should not have had enough power to join the Espada. However, he still did because his power allows him to have infinite evolutionary potential, and that this power came from the Hollow who possessed Kaien, Metastacia, whom he devoured, meaning that his Zanpakutō's ability is the power to devour dead Hollows and gain their abilities. He then takes off his glove, showing a deformed arm as his Zanpakutō. Aaroniero then states that the nostalgia Rukia has been feeling isn't just her imagination, because this body really is Kaien's and that he acted accordingly after gaining all of his memories.

Aaroniero decides to show Rukia what an Espada's Resurrección is like, and releases his Zanpakutō, Glotonería. He explains that this is the form of all the Hollows he has eaten and that his Resurrección can use every single Hollows ability at the same time. He then states that he has eaten 33,650 Hollows so far and that Rukia should think of this as her fighting against an army of over 30,000 Hollows. Rukia apologizes to Kaien for everything she has done to him and then goes to fight Aaroniero. She jumps up and attempts to stab Aaroniero but is sent flying back in the air. Aaroniero then uses Kaien's Zanpakutō and attempts to stab her as well, but Rukia uses what little strength she has left to block the attack with her own Zanpakutō. However, the Zanpakutō breaks in half and Rukia is skewered through her stomach. Aaroniero begins to laugh madly and Rukia begins to have memories of Kaien.

Memories of Kaien
Rukia is daydreaming and Kaien slaps her on the head to wake her up. The two of them then argue and Kaien tells her to hurry up. Rukia thinks to herself that this place is Mt. Koifushi and that she remembers every single aspect about the area as this is where Kaien first trained her. The two of them reach their destination, and they begin their training. However, Rukia is distracted by a bird and she is easily beaten by him. Her stomach then begins to growl, and Kaien takes this as a sign that she wants him to buy lunch. The two of them then eat and Rukia wonders why she's even in the Gotei 13, since she believes her power is insufficient. Kaien tells her that the reason she's here is to serve and protect, but Rukia wonders what there is to protect. Kaien tells her there are a lot of things to protect but Rukia asks him for a less vague answer. However, he states that there isn't and tells her their captain's philosophy on this matter, which is that there are only two types of battles, ones to protect your life, and ones to protect your pride. However, Kaien believes that when it comes down to it, both of those battles are for the same thing, which is the heart. Rukia tells him that what he said was corny, which angers Kaien. He then asks her where she thinks the heart is, but Rukia points to where her heart physically is. Kaien goes up to her, forms a fist, and tells her that he thinks the heart is right here. He explains that the heart is born when you interact with someone and that if she were the only person in the world, there wouldn't be a heart anywhere. He then tells her that when you fight, the one thing you must never do is die alone, since if that were to happen, your heart would never carry on to your companions.

Aaroniero tells her that no matter how hard she tries it won't change the fact that she can't cut him down. However, Rukia grabs onto the Zanpakutō currently skewering her, and brings her broken Zanpakutō up to Aaroniero's face. He tells her to give up, but Rukia uses San no mai, Shirafune, and her Zanpakutō reforms, causing it to go straight through Aaroniero's face. His true face then appears, and Rukia tells him that while he has Kaien's body, his heart was left with her and says farewell to the Espada. She then swings her Zanpakutō up out of the cylindrical capsule, causing it to break.

Aftermath
The two Hollow heads are sent out of the glass cylindrical capsule they were concealed in and Rukia and Aaroniero both fall to the ground. One of the Hollow heads begins to yell for Aizen's help and then feels betrayed since Aizen promised him that there would be no more pain, while the other one curses Rukia with its dying breath. The two Hollow heads then crack in half, killing them. Rukia tries to leave the room she's in and thinks to herself that she can't die alone and remembers her friends. She then remembers Orihime, and states that she knows the loneliness of being a prisoner, the joy of your friends saving you, and the fear of them getting hurt. She then hopes for Orihime not to be fearful and that she's coming to save her. However, Rukia collapses on the ground unconscious.