Arina is a ten-year-old fourth-grade student at Hosea Academy, appearing as a minor character in the series. She possesses short, straight dirty blonde hair and olive-green eyes, accentuated by a pair of circular glasses. She is most often seen wearing her school uniform.

Despite her youth, Arina carries herself with a mature demeanor, though she shares certain traits with her friend Kurumi. She holds Haruhiko and the rest of Team E in high esteem, considering them reliable after Kurumi praised them.

Her role in the story begins when her cat, Rudolph, goes missing. She turns to Kurumi for help, who then involves Team E. The team manages to locate Rudolph inside a cat mansion, following the resolution of complications involving the mansion and a Phantom. Arina is overjoyed at being reunited with her pet and expresses her gratitude by offering to assist Team E in cleaning the mansion.

She shares a strong, supportive friendship with Kurumi Kumamakura, feeling comfortable enough to seek her help in a time of need.