Kaoru Setouchi (瀬戸内 薫, Setouchi Kaoru) is a classmate of Iori Nagase, Taichi Yaegashi and Himeko Inaba. Initially antagonistic towards Iori, Setouchi later resolves to better herself as a person and is voted Class Representative during her second year. She wants to join the student council. She plans on going to Prefecture S to study at a social science college that researches on cities and villages.
Setouchi has long light brown hair, dark brown eyes and wears a pair of earrings with butterfly designs. Setouchi prefers to keep her uniform's shirt untucked and neglects to wear her uniform's ribbon. At the end of the Michi Random arc, Setouchi dyes her hair black and cuts it to shoulder-length.
Early in the series, Setouchi is depicted as irritable and short-tempered. She has proven to be a fairly audacious character, not afraid to pick fights with others if her buttons are pushed and unforgiving if wronged.
Behind her tough exterior however, Setouchi, in truth, is a very submissive individual who is easily influenced to do out of character things if she feels pressured by her peers. She dyed her hair due to pressure from her previous boyfriend. She is, at heart, a genuinely nice girl who simply wants to be respected and accepted, but she is often misguided in her endeavors.
- Shouto Shiroyama: Setouchi has a crush on Shiroyama and her feelings are so strong that Iori rejecting Shiroyama's confession was enough to make Setouchi have a personal vendetta against Iori, partially out of sympathy and partially out of jealousy. By Asu Random II, the two have begun dating, but their relationship is put to the test by the phenomenons they face in the Isolation Dimension.
- Iori Nagase: A female classmate. Throughout the series, Setouchi and Iori are shown to have a difficult time getting along for one reason or another. Their antagonistic relationship comes to a head during the Michi Random arc when Setouchi hires thugs to vandalize the Cultural Society's clubroom to get back at Iori for rejecting Shiroyama. After the case is settled, Setouchi and Iori set aside their differences and the become friends.
- Setouchi's earrings are shaped like butterflies.
- Butterflies in many cultures are symbols of change for the better.