A mysterious girl who claims Arata to be her husband. She looks like Hijiri, Arata's cousin and childhood friend. Arin rarely shows emotion, and cares little what others think of her. Her first meeting with Arata occurred when she was bathing in the men's bath because she preferred the quiet (very few men attend the academy due to the fact females are usually more attuned to magic) despite being discovered by Arata she acts casual as if nothing had happened. Although she shows little emotion of her own she is quick to notice it in others. Arin has no memory before the age of 8 she remembers a void of nothingness, slowly becoming aware of the world around her she began to cry, then started wandering and eventually was discovered by the headmaster who took her to the school, she has been there ever since.
Arin believes herself to be the magic king/demon lord's wife although no official marriage has been arranged, thus she becomes quite jealous of anyone flirting with Arata, however she has stated that she doesn't mind the trinity seven because they are all friends. As time progresses Arin starts to show a little more emotion, such as smiling and blushing when speaking to Arata, the other trinty seven members have commented on this saying that they prefer this side of her.
Arin's Magic is mostly spell based. her branch is chaotic rune which is said to manifest the power of the gods, her magic is capable of overpowering the magic king/demon lord canadit's power once enhanced, and is activated by writing Norse runes in the air. Her magic is highly compatible with Yui's arc symphony.