An Onoya is a 27-year-old employee of the ReLIFE Laboratory's Support Division at the Kantou Branch. During the 2013 academic year, she goes undercover as a third-year transfer student at Aoba High School, using her small stature, light brown hair often worn in braids or worn loose and wavy outside of school, and a pair of non-prescription glasses to blend in as a teenager. She originally recommended Arata Kaizaki as a candidate for the ReLIFE experiment, but due to her incomplete training, his supervision was reassigned to her senior colleague Ryo Yoake. She later assumes responsibility for monitoring the other test subject, Chizuru Hishiro, starting in the second term. Before joining ReLIFE, she worked in retail apparel but faced workplace challenges; after anonymously contacting the laboratory's counseling hotline as "A-san" with her counselor "Y-san," she resolved to join the organization to help others and was surprised to discover the secret nature of the experiments. Onoya presents a cheerful, bright, and friendly exterior, but this masks a more calculating and manipulative side. She tests subjects in various ways, including attempting to seduce Kaizaki simply to observe his reaction and pretending not to know Yoake while at school. She intentionally performs poorly on entrance exams to create opportunities to study with Kaizaki and frequently inserts herself into his social circle. After her cover is blown, she maintains her disguise by claiming to be a support staff member in training. With Yoake, she shares a complex dynamic, teasing him frequently while holding him in high professional regard and showing genuine concern for his well-being, with hints of deeper feelings. As Hishiro's supervisor, she works to help her succeed and form social bonds, though she is saddened by the knowledge that Hishiro will likely lose the personal growth she achieved. Onoya is perceptive about interpersonal relationships, an excellent cook, and has a refined sense of personal style from her fashion industry background. She underwent ReLIFE training herself during the 2012 academic year, where she observed Yoake's struggles with a previous subject and helped him regain confidence.