Arin Kannazuki/Relationships

Royal Biblia Academy
Arata Kasuga - As the partner of the Magic King, Arin cares very deeply for Arata and as well loves him, becoming quite attached to him since his arrival. She often calls him her husband and considers them to be already married. Arin first met Arata in the men's bath unclothed, although she was rather nonchalant during the whole experience. However, because of the nature of their relationship, Arin developed a strong interest in him mainly for her research. While on the other hand, Arata was unsure how to interact with her due to her blunt personality and identical appearance to Hijiri. Regardless, the two of them quickly became good friends, even after Arin trapped him or even caused him to create a Breakdown Phenomenon. Arin does not mind Arata's shameless personality, even willing to comply with some of his desires. Likewise, he has also become used to her, appreciating her support and guidance. Although, they sometimes still find aspects of each other surprising and troublesome as well. Notably, since meeting Arata, Arin has slowly begun to change from her usual emotionless behavior, showing more different emotions which have been noticed by her friends. Both of them genuinely care for one another, willing to support and protect each other during dangerous situations. Arin's attainment of the Demon Spear Gae Bolg was largely due to her determination to protect him. Also, Arin can become jealous whenever he interacts with other girls but is more or less fine with her friends in the Trinity Seven.

Trinity Seven
Lilith Asami - As members of Trinity Seven, Arin and Lilith are good friends and usually get along very well. Although, due to Arin's straightforward character and lack of common sense, Lilith often times has to correct her actions and behavior, which Arin usually finds difficult. Despite this, the two of them care for one another, willing to fight and protect each other. Furthermore, while Arin is sometimes jealous of Lilith's closeness with Arata, she actually does not mind and both of them continue to remain on friendly terms.

Yui Kurata - Yui and Arin are good friends, both willing to fight and protect one another. When Yui's magic becomes unstable and causes a Breakdown Phenomenon, Arin is one of the people who helps save her. Also, despite the two being interested in Arata, they still remain on a friendly term. Although they sometimes get jealous of each other's interactions with him. At one point, Yui has stated that she was willing to be his mistress because Arin was his partner. During battles, both of them have been shown to have excellent teamwork as their magic complements each other. For the Magic Research Showdown, they were paired together as a team and faced off against Arata and Lieselotte. With their combined efforts, they would control the majority of the match and greatly overwhelm their opponents. Finally, Arin, with the support of Yui, would achieve the Trinity, defeating Arata and Lieselotte. Their teamwork has been noted to specialize in defense.

Iscariot
Hijiri Kasuga - Arin and Hijiri are believed to have an unknown connection due to their very similar appearances and magic. Both of their Thema's are Ruina from the Ira Archive and they also utilize the same Chaotic Runes magic. However, their personalities are quite different as Hijiri displays more emotions than Arin. Furthermore, as members of Iscariot and the Trinity Seven respectively, Hijiri and Arin are enemies although they are willing to work together due to their strong devotion to Arata. When Hijiri was about to destroy Arata and Lilith, Arin gained the Demon Spear Gae Bolg to break downtime and space in order to save them. On another occasion, after Arata became trapped by Anastasia-L, Arin willingly agreed to ally herself with Hijiri regardless of her past actions, trusting her rival because of her real feelings. While the two girls are competing for Arata's affection, they nevertheless have respect for one another. Notably, despite their interactions, neither of them have commented on the unusual circumstances behind their identical appearance. Furthermore, Arin's possession of Gae Bolg allows her to nullify magic from the Ira Archive, making her a natural opponent to Hijiri.