Arisu Sakayanagi is one of the class representatives of class 1-A along with Kōhei Katsuragi. She suffers from congenital heart disease which limits her physical ability.
She appears as a petite teenage girl with lilac-coloured hair and violet eyes. She wears a black beret on her head with a grey ribbon connected to it and wears the standard school uniform. She often walks with a cane due to her health condition.
She appears to possess a "go with the flow" attitude as she accepts most situations with no protest though she voices her dislike of boring situations after Katsuragi noted of the class scores. Unlike Kōhei Katsuragi, who has a conservative stance, Arisu possesses an innovative attitude. Together, the pair effectively lead class A through the school years.
She enjoys situations she finds interesting as shown when she smiled at Kakeru Ryūen's declaration to rule the school or when she listened to the speech of Suzune Horikita and found it amusing. In the light novels, Arisu enjoys toying with people as seen when she cryptically hinted to Kiyotaka Ayanokōji of knowing him while he had voiced he never saw her before. Later on, while being together with Honami Ichinose, she also had the chance to show her confidence and complacency after Teruhiko Yukimura of Ayanokōji Group boldly claimed that D-Class has the plan to overtake A-Class soon.
Additionally, although she has an easygoing personality, it was shown in the later part of the series that she's easily provoked when being described based on her petite appearance (e.g. "Little Girl") as she believes that it doesn't give her justice due to her domineering quality.