Arima has the appearance of a young man, though he is really in his mid-forties.
He is a tall man who wears glasses and has long white colored hair with blue ends. His eyes seem to be amber colored. He is mostly seen grinning. He is first seen wearing only underwear during his first appearance, which is why Rokuro always calls him "Perverted Underwear Man".
When pushed to the limit in fighting the second Basara, Sakanashi, Arima left with no choice employed a curse to transform into a Fallen Impurity. In this state his size remains unchanged while his appearance changes drastically: like Yuto Ijika his skin took on a darkish hue while his face turned gray. His hair in this state lightened considerably while four uneven horns adorned his head- the longest covering where his right eye had been and creating cracks down his face.
Disimiliar to Mystic Gear Equip or Impure Death Equip, Arima's form from the head down is darker with several sharp points focused along his back, shoulders, waist and knees. An exoskeleton akin to a twisted plant with various portrusions from most points of his body wih his kuji-kiri appearing on his abdomen.
Arima is a cheerful guy who seems to like having fun. A running gag in the series; he often gets in trouble, resulting in him running away from troublemakers. Despite this, he is actually a serious person, although in a sarcastic manner. He is also displayed as a kind and caring person, this was shown when he was genuinely worried about his 'henchmen', Rokuro and Benio. He is also stated as 'a tighty whity weirdo' by Rokuro.
However, when it comes to his son Arimori, Arima displayed a more serious tone to him speaking him to bluntly about his lack of talent as well threatening to disown him from the family when he joined the Enmado House. This was shown to be far from detachment, as he comforted Arimori when he found his son at his mother's grave mourning her.
Arima's true nature was found by some of the Twelve Guardians like his acquaintances since youth, Seigen Amawaka and Arata Inanaki, and later other ones like Shimon Ikaruga - by fair means or foul, the only thing he wanted is the victory over the impurities. Even his son and himself, are less important to ones who are critical to the plan, the two chosen ones cursed with special power. As a result of that, Arima is also adept at manipulating others to reach the goal.
Arima likes to flirt with women, but he also has true feelings to his deceased wife Mana.
Arima is also somewhat narcissistic, as he makes the Christmas of the Tsuchimikado Island his own birthday party.
When Rokuro started to undergo a transformation during his fight with Yuto, he was suddenly engulfed in a light and lost consciousness, just as Arima appeared through a gate greeting Yuto. Which means, he faked his death. Arima confirmed that he survived and used a spell to bind Yuto. Yuto broke free relatively easily, though it was really a diversion for Arima to use a spell to remove the barrier Yuto placed around Benio. Then, Arima took Rokuro and Benio through the gate he used to appear, to escape to the real world.
Arima arrives at the Enmado House, where he shares a jovial greeting with Rokuro who questioned him on his presence. However, Arima drops his good tone to tensely greets hi son and berates him for his actions while telling him that he no unique talent. He threatens to banish him from the Tsuchimikado House if he does not return. As Arimori tries to work up the courage to reply, Rokuro steps in and calls Arimori his family since he decided to come to his house. He tells Arima that since he brought up disownment then Arimori can join him to Kinako's shock. A tough talk between Arima and Rokuro breaks out, while Arimori is barely able to get out one word before his father reminds him that one must have a strong resolve in order to lead the Tsuchimikado House. Afterwards, Arima leaves and speaks to his late wife by saying things are not going well without her.
After the explosion, Arima lays on the ground partially human again before his son approached him.
Powers and Abilities
Originally, Arima shows no indication of any actual fighting strength. However, his abilities are befitting of his status as the Exorcist's head. During the conflict between the two basara, he disposes of a huge amount of impurities effortlessly, protecting Mayura and Benio. Despite the fact that he came with 2 of the 12 Commanders, he went to Magano alone, as the commanders deemed that they'd just get in the way, a testament to the full extent of his abilities. It is implied that he may have power and skill greater or equal to the Kijin and Toda. His full testament of his abilities is proven where he easily defeat Shiromi five Basara with ease and fight equal grounds and even manage to gain upperhand slightly against Sakanashi second Basara and Strongest of all current Basara.
- Senku Kamaitachi (剪空鎌鼬 Senkū Kamaitachi?, lit. "Kamaitachi Sky Cutter"): 
- Shugo no Iwafune (衆合岩舟 Shūgō no Iwafune?, lit. "Storm of the Stone Dreadnoughts"): 
- Kakaiju - Kongo Shusai Shokonpon Daidarani - Dai Kasho Zanmai (火界呪・金剛手最勝根本大陀羅尼 大火生三昧 Kakaiju - Kongō Shusai Shōkonpon Daidarani - Dai Kashō Zanmai?, lit. "Fire Realm - Vajrapani Prime Subjugation Grand Spell - Samadhi within the Great Flames"): 
- Dai Kyokan Mato Hyosatsu (大叫喚魔凍氷殺 Dai Kyōkan Matō Hyōsatsu?, lit. "Glacial Purge of Mahaaraurava"): 
- Kakuheki Shaan (隔壁遮闇 Kakuheki Shaan?, lit. "Dark Shrouding Partitions"): 
- Soten Mugen Kaina (総天無限腕 Sōten Mugen Kaina?, lit. "Divine Infinite Arm"): By using the charms Zanyo Enrai (惨陽炎來 Zan'yō Enrai?, lit. "Fire of the Appalling Sun") and Gekka Hyojin (月下氷塵 Gekka Hyōjin?, lit. "Ice Dust of the Moonlight"), Arima can equip his Shikigami Pochi and Tama as gear for his arms.
- Renge-O - Senju Sengan Kanzeon Bosatsu Modarani - Issai Shujo Gokuraku Ojo (蓮華王・千手千眼観世音菩薩姥陀羅尼 一切衆生極楽往生 Renge-Ō - Senju Sengan Kanzeon Bosatsu Modarani - Issai Shujō Gokuraku Ōjō?, lit. "Lotus Monarch - Dharani of Avalokitesvara with One Thousand Arms and Eyes - Peaceful Death of All Living Beings"): 
He was shown to be exorcising impurities without doing anything and using shikigami to track down Kuranashi, a very elusive Basara. Arima seems to specialize in Ice and Fire techniques and has very immense spell power to the point where he almost defeated Kuranashi with one blow, leaving a gargantuan crater in it's aftermath. He was presumed to be dead when Kuranashi buried him under the ground with a Seiman.
- Barrier Release (結界解放 Kekkai Kaihō?): By preparing beforehand an array of charms, Arima can neutralize any barrier, no matter how resilient, using the Five Elements principle to do it.
- Pursuit of Ages Ritual (
時律利不府之義Tokitsurifunogi?): Arima triggers this ritual during his battle against Kuranashi, that involves temporarily separating his soul from his body in a life-and-death situation to be able to revisit past events. Arima uses it to learn about what Abe no Seimei did.
- "The darker the darkness is, the brighter the stars shine."
- The name Arima means "exist" (有) (ari) and "horse" (馬) (ma).
- Twin Star Exorcists Manga: Chapter 65
- Twin Stars Exorcists Manga; Chapter 63, page 9.
- Twin Stars Exorcists Manga; Chapter 63, page 13.
- Twin Stars Exorcists Manga; Chapter 63, page 20-23.
- Twin Stars Exorcists Manga; Chapter 63, page 29-30.
- Twin Stars Exorcists Manga; Chapter 64, page 6-7.
- Twin Stars Exorcists Manga; Chapter 64, page 8.
- Twin Stars Exorcists Manga; Chapter 64, page 10.
- Twin Stars Exorcists Manga; Chapter 64, page 10.
- Twin Stars Exorcists Manga; Chapter 64, page 12-14.
- Twin Stars Exorcists Manga; Chapter 64, page 20-21.
- Twin Stars Exorcists Anime; Episode 42.
- Twin Stars Exorcists Anime; Episode 43.