Arumi has the appearance of young girl with white long hair that has two green hair ornaments on the sides and purple eyes. She has a large chest which many point out. After joining Tsuzura Temple, her hair ornaments now have tassels.
Arumi is a normally a quiet and modest girl. She gets easily flustered when approached with lewd situations. However, when it comes to her feelings for Akito, she desires a more romantic and sexual relationship with him but hides from him.
Arumi, Akito and Hifumi were tools from the same residence that had been used for over three generations. All three became tsukumogami at the same time, becoming sworn siblings living with their master. At first they lived peacefully, but soon their master began abusing Hifumi's ability to manipulate fate, exhausting her power and having the side effect of turning some of her user's into monsters. Hifumi had pleaded with him to stop to no avail, prompting Akito and Arumi to inform the villages of his actions. The villagers formed a mob, killing their master but destroying Hifumi as well. The villagers then turned on Akito and Arumi, prompting Akito to kill them all in self defence and forcing Arumi and Akito to wander, jumping from master to master. While doing, they gradually lost faith in humans, and after escaping their fourteenth master, they found a red bowl in a river which opened a door for them leading to Mayoiga.
Upon entering Mayoiga, the two were immediately met with hostility by Yasuki who attacked them. Arumi and Akito defended themselves before Mimane arrived, interrupting their fight and barraging the pair with questions. The two were brought to Tanmen who formally welcomed them to Mayoiga. They lived peacefully in Mayoiga until one day two residents lost their power and reverted back to their original forms. It was then that Tanmen decided to tell the two the truth behind Mayoiga, about Miurahi, their past Iwanagahime and their plans to obtain a new Stone Shard, asking the two to aid them. Having grown attached to their new family, the two agree to aid Mayoiga, Arumi using her ability search for the best course of actions and candidates to obtain a Stone Shard from. After nearly thirty years of relying on Arumi's predictions to no results, Genbu and some others began to protest. After the protest was quelled, Arumi's used her abilities, revealing a black mass which she, Akito, Yasuki, Mimane, Shinshou and Chikage went out to capture. After capturing the mass, a few more years passed before Azami would reveal herself and give Mayoiga instructions for obtaining a Stone Shard. This lead to Azami's plan which had Arumi, Akito, Yasuki and Mimane infiltrate Kamioka to cause aberrations to weaken Kukuri. The four infiltrated Kamioka East Middle School and became students there, residing in an empty classroom as their base of operations.
During the incident with Mana Manaka's shoe amasogi, Arumi uses Peaking Ahead and decides helping Kazuya Kagami resolve the problem to be the best course of action.. Arumi appears to Kazuya in the boys' washroom, telling him a fairy tail as a clue to investigate the shoe amasogi and disappears before Kazuya can respond to her story. Kazuya believes Arumi to be a ghost and runs out of the washroom scared.
After the destrion of Mana's amasogi, Akito, Yasuki and Mimane discuss their next plan in the classroom. Arumi remains silent and Mimane ends up going ahead with her plan to give Isuzu Iriha a dream pillow amasogi. After the amasogi is destroyed, Mimane complains about being bored and wanting to eliminate Kazuya and Kiriha herself. This causes a fight between Azami and Yasuki which Akito stops.
After Akito returns from the Arcade with Mimane, he reveals to them that Mimane had revealed her identity to Kazuya and Kiriha. Yasuki tells them to avoid the two as much as possible. Later in school, Arumi tells Akito that Mimane's new amasogi has been put into action but before Akito and Arumi can leave the school they are greeted by Kazuya and Kiriha. Wakana Wakisaka's suddenly sucks the four of them into a empty room. Here Arumi introduces herself as Akito's sister, who Kazuya recognizes from the washroom from before. Akito confronts Arumi about this in private, and warns her about using Peaking Ahead without telling him since it can only be sued once a month. After searching around the room with no exit, Wakana reveals herself the explains the nature of her love sugoroku quiz amasogi, forcing them to play along. Throughout the quiz, the two pairs are forces to answer increasingly private and erotic questions about their partners. While Arumi and Akito are initially set back, they end up catching up to Kazuya and Kiriha at the end goal, with Arumi having lost most her clothes from answering incorrectly. Wakana presents the final question being who does the male love the most. Kiriha answers incorrectly and is sent back to the beginning. Akito ponders for a bit before Arumi answers for him. It is suggested that the answer for Akito was Hifumi. Since they had reached the goal, Wakana destroys her amasogi and they are sent back to the school.
Akito later tells the group how he was blackmailed into joining Kazuya's club along with Mimane. While Akito and Mimane are dealing with their first case for the club, Mimane finds Arumi to scan her appearance. Arumi is furious at Mimane upon finding that she had mimicked her appearance in order to use Arumi's naked appearance as bait. Mimane's bait fails and she suggests that the two of them get naked together to improve its effectiveness. Annoyed, Arumi tears off Mimane's clothes, telling her to get naked by herself, incidentally luring out the amasogi host. Their target Kukuri later comes by and embarrasses herself in front of them.
Later that night, Mimane returns from staying over at Kauzuya's house to inform them that members from Mayoiga have begun to attack. While Yasuki suggests they help the attackers, Mimane tells them that Kukuri is still too strong, forcing Akito and Mimane aid Kazuya and Kukuri against Mayoiga. After the assassins are defeated, as Akito and Mimane walk home, Arumi finds the and tells them a revolt has occurred within Mayoiga. Arumi, Akito, Yasuki and Mimane return to Mayoiga and are confronted by Sanjuurou. After eliminating him, Chikage arrives to greet them and Mimane accidentally knocking over a large mud sculpture onto the girls. While Akito and Yasuki speak to Tanmen, Arumi and the girls go to take a bath.
After debriefing with Tanmen, he has Arumi use her divination which reveal two stone shards, prompting Tanmen to reawaken Miurahi. With Miurahi awakened, him and Tanmen announce Mayoiga will now begin their full frontal assault to take Kukuri's stone shard. Mayoiga launch their invasion via a giant flying boat which is intercepted by Honoka. Mimane creates an illusory duplicate of the boat and its passengers to distract Honoka while Miurahi sneaks past to Hakusan Shrine with a small group. Arumi and Akito join Miurahi's group. Prior to engaging Kukuri, Miurahi has Arumi use her divination to confirm his choice to fight Kukuri one-on-one is the best choice. Miurahi has Akito and Arumi hide in the bushes, using her divination to watch out for negative outcomes. Arumi and Akito are shocked upon witnessing Miurahi be suddenly killed by Azami during his battle and using his stone shard to revive Kanaka Kagami. Akito is frustrated that they were unable to foresee Azami's betrayal despite their abilities to which Arumi suggests they may have been manipulated from the start, ever since seeing the black mass her divination. The two watch as the other members of Mayoiga are effortlessly defeated by Kanaka. Akito attempts to use Arumi's Lunar Ecliptic Prediction to look for an opening to no avail.
After the battle ending with Kanaka being sealed away, Arumi and Akito along with the other Mayoiga tsugumomo were taken to Tsuzura Temple and were separated. Masuji Madarai use Arumi's ability to rewatch Kanaka's battle and Kukuri's death. Some time after obtaining the puppet bindings, Madarai uses them on Arumi and Mimane. Enhancing Arumi's power with the puppet binding, Madarai looks three years into the future after Kanaka's release, witnessing a vision that Arumi herself could not see. Madarai also uses Arumi's divination to ensure his faction is victorious in the Nine Masters Tournament. After Takumi Tagusari's defeat in the tournament, Madarai summons Arumi and Mimane to complain about how Arumi's prediction was wrong to which Mimane explains that he had misused her ability. In the final match of the Nine Masters Tournament, Madarai uses the his puppet bindings and his tsukumogami Chuushingura to fuse himself with Arumi, Mimane and the remaining Mayoiga tsukumogami, transforming himself in a deformed amalgamation of people. Upon seeing Madarai do this to Arumi and Mimane, Kazuya becomes enraged and subconsciously uses Domination on Kyouka. Madarai uses Arumi's abilities in his fight, causing her to scream in pain whenever she does so. Kazuya defeats Madarai with the help of a revived Kiriha, freeing Arumi, Mimane and the others. Upon recovering the Arumi and the remaining Mayoiga tsukumogami, Ouhi finds their souls had been too damaged by Madarai's fusion, forcing her to make a deal with Madarai to have hime Chuushingura again in order to repair them. Arumi and the Mayoiga tsukumogami are saved, and Arumi reunited with Akito.
Ouhi and Ouna become Arumi's temporary owner and they have Arumi perform a divination to ascertain the best training method for Kazuya and his new partners, resulting in his first assignment to deal with Mami Mamisaka's case. Some time after Kazuya's return, Ouhi and Ouna have Arumi use her monthly Peaking Ahead ability to ensure the situation with Kanaka's seal remains stable for the foreseeable future. Arumi asks them of the current situation with finding owners for the Mayoiga tsukumogami. They explain some have been made dormant to conserve their energy until they find a suitable owner, and tell her of Akito returning from an assignment with his new owner. At the entrance to Tsuzura Temple, Arumi's awaits Akito's return with his new owner Hijiri Hijiogi and stares menacingly at her when they meet. Later on, Mimane mocks Arumi for her jealousy and Arumi has Mimane take the form of Akito so she can relieve some stress. Mimane leaves to find Akito and copy his appearance. Unbeknownst to Arumi, the real Akito arrives and Arumi begins making sexual advances on him. Mimane returns being unable to find Akito and Arumi suffers the horrific realization of the mistake she has made. Later on, Arumi has Mimane fulfill her request, double checking to make sure it is Mimane. This activity continues for a while, with Mimane complaining to Shinobu that Arumi has her do it twice a day.
Heaven Hand Ball (
- Peeking Ahead (
先覗占, Senshisen): The name of the technique Arumi uses to look into many futures such as a possible and/or desirable future but it comes with many limits and flaws. She is only able to use it once per month and until the day the future actually happens. In addition, the further away in time or space she looks, the less accurate her future reading becomes.
- Lunar Ecliptic Prediction (
白首予知, Hakudoyochi): An ability that allows Arumi to see two seconds into the future, allowing her to foresee and respond to immediate upcoming events. Arumi cannot take action while using the ability.
- Past Event Replay: Arumi has the ability to replay past events. Masuji Madarai and Suguru Susuzumi had used Arumi's ability to rewatch the reawakened Kanaka Kagami's battle.
Mental Sight Bind (
|Leaders||Miurahi † • Tanmen|
|Members||Akito Ashimine • Arumi Ashimine • Azami ‡ • Chikage • Genbu • Guramon • Jungou • Kyouka • Mifune • Mimane Miyou • Rokkaku • Sanjou • Sanjuurou • Sarara • Senga • Shinobu • Shinshou • Sosogu • Tsuchishiro • Urara • Yasuki Yatsukawa|