She is voiced by Megumi Han in the Japanese version and by Cassandra Lee Morris in the English version.
Benio is a teenage girl around average height and green eyes. She has waist-long black hair (dark purple in the anime) that has a set of long bangs that frames her forehead. She is usually seen in her school uniform or exorcist gear. She used to have two pink bobble hair ties (given by her brother Yuto in anime), on both sides. She later replaced them with a pair of silver Japanese bellflower-shaped hair pins that were given to her by Rokuro.
During their fight against Yuto, she loses both legs and gets impurity legs as replacements, much like Rokuro's right arm.
Two years later, she is shown to have grown taller, however her breasts were still quite undeveloped.
After her transformation to Taiyin, as a humanoid impurity, she has her kuji-kiri on the stomach, dark skin, golden eyes and light-colored hair like other impurities. She has a single horn on her right side, and a long mantilla on her hair. The hair pins given by Rokuro are transformed into neck and head decorations.
Benio first comes off as a cold, quiet person, who dislikes talking and is easily irritated. However, regarding exorcism she is very passionate and can be very talkative. Since she comes from an important family, honor and pride are both very important to her. She is also very competitive, especially around Rokuro, and since she was taught to never back out from her words, she can be pretty stubborn and will use any argument to win.
After warming up to Rokuro, Benio is shown to actually be a very caring person. She is also easily embarrassed, even to the point of fainting when she's extremely embarrassed.
She also really loves ohagi, and is even prepared to make an anime adaption of ohagi man, a hand-drawn manga based solely around ohagi.
After two years, Benio seems to be able to show her feelings comfortably compared to when she first met Rokuro, and seems to show her jealousy more openly than before.
Benio was born raised in Adashino House on Tsuchimikado Island to learn and practice exorcism for her future as an exorcist and lived a happy life, until a powerful impurity defeated her parents at the sight of her own home. This Basaraproceeded to ask her whether she wanted to save her mother or her father, and when she could not answer, asked her parents whether they wanted to save themselves or their daughter, to which they answered without hesitation, orphaning her on sight in front of her. Then later, it was shown that she cried heavily at their funeral.
Four years later, Benio heard her brother Yuto disappear in the Tragedy of Hiinatsuki Dormitory, furthering her emotional pain.
Before the events leading up to the beginning of the story, Benio had trained herself to become an exceptionally powerful exorcist, wielding her late mother and father's weapons. She later moved to Kyoto to live with her relatives of Adashino House and attended middle school normally Before long, she and her caretaker Kinu were assigned to move to Tokyo, and she had to leave her old life behind.