Yashio Rui is a second-year student at Tsukinomori Girls' Academy and the violinist and composer of Morfonica. Rui has dark brown hair that goes just past chin-length and thin, brownish-red eyes. Her bangs are parted to her left and go down past her chin. Part of her bangs goes between her eyes, down to the base of her nose. Despite only being a high school student, Rui looks mature for her age. Rui is a talented individual who is always at the top of her class. She has a dry personality and is always aiming for top results, and speaks in a polite manner. She is very logical and realistic, but can also be blunt when it comes to her opinions, especially about talents or music. In addition to her logical nature, she plans out her days and schedules very thoroughly, and as such, doesn't understand things like people hanging out or taking detours after school. Due to her stoic and composed look, Rui says that people tend to think she's angry even when she's not. In reality, the reason why Rui does not choose to immerse herself in activities she deems meaningless is because she is afraid of getting hurt and disappointed in the same way she did after placing 5th in the competition that made her decide she doesn't have true talent. She felt that no matter how hard she practiced, no matter how much she felt like she loved music, her talents weren't acknowledged because she didn't have it in the first place. This is also why she developed a cut-throat attitude and refuses to prioritize her emotions similarly to the other Morfonica members. Although Rui is the kind of girl who wants to follow rules and ensure that everyone does as well, she will stand up for her friends and bandmates, such as shown in Morfonica's First Band Story and Lost Butterflies' Tritone. In the former, she stops some Tsukinomori students trying to steal the classroom the girls used for practicing, while in the latter, she attempts to convince Tsukinomori's new principal to reconsider her ban on anything that isn't related to studying, as she believes it has caused nothing but confusion and discord in the school, and as the student council president, it's her job to voice out the students' concerns. Despite having very opposite personalities, Rui later befriends both Kaoru and Masuki, bonding over art and music appreciation.