Serino Mihara is a classmate of Aiko Morimura, sharing her age and academic setting. Her background as the daughter of a wealthy family informs her initial portrayal with snobbish tendencies, evident in her interactions and her dynamic with her pet, a female Siamese cat named Cat. The cat mirrors Serino's perceived sophistication and selective social preferences, becoming a focal point for comedic romantic subplots by attracting the affections of Spank the dog and rival cat Torakichi.

Serino's personal ambition is to become a professional ballerina, a dream serving as her driving motivation and showcasing her dedication and perseverance alongside her more superficial traits. While early depictions cast her in a somewhat antagonistic light towards Aiko, later developments reveal greater complexity. She participates in group activities with classmates, such as an excursion to the Tateshina plateau. On this trip, her cat goes missing due to Spank's error, leading the cat to develop an affection for a ranch guard dog named John, much to Spank's dismay.

Demonstrating a shift towards inclusivity, she hosts events like a group barbecue during the plateau trip, moving beyond her initial aloof persona. Her presence in these social settings alongside recurring characters like Ryo and Shinako indicates integration into the peer group despite early friction. Her wealthy status remains a consistent trait, influencing her lifestyle and occasional condescension, balanced by her commitment to ballet and gradual participation in shared experiences.