Chie Hoshinomiya is the homeroom teacher for Class B at Advanced Nurturing High School, her own alma mater. She shares a past there with Sae Chabashira, whom Chie considers a friend, though Chabashira denies any closeness and criticizes Chie's flirtatious behavior towards students like Kiyotaka Ayanokōji. Undeterred, Chie persists in such conduct, reflecting her flirty and easygoing nature. She harbors a long-standing personal vendetta against Chabashira, stemming from an unresolved incident during their student days, driving her to actively hinder Chabashira's class from reaching Class A. Physically, Chie possesses an average height, light-brown chest-length hair curled at the ends, purple eyes, and a slim yet well-endowed figure. Her demeanor is friendly and approachable. She engages in frequent drinking, often leading to hangovers during school hours that occasionally impact her teaching duties. Despite this, she is insightful, capable of recognizing student potential early, such as identifying Kiyotaka Ayanokōji's hidden capabilities despite his Class D enrollment. She closely monitors his mathematical skills, physical abilities, and appearance. While stating she doesn't dislike students like him, she explicitly declares she would hate him the most if he became her enemy. Her relationship with fellow teacher Tomonari Mashima is notably close; they consider each other best friends and comfortably discuss personal matters, including love interests. Professionally, she initially supported her student Honami Ichinose, recognizing her intellect and leadership. However, after Ichinose's repeated failures in special exams and inability to secure victories against other classes, Chie grew disillusioned. She openly expressed distrust and dissatisfaction with Ichinose's leadership, complaining to colleagues that Class B—now demoted to Class C under her watch—was incapable of reaching Class A, marking a significant shift from her earlier optimism. Chie employs pragmatic tactics to strengthen her class, like strategically assigning Ichinose to the Rabbit group instead of the Dragon group during a cruise ship exam to better observe Kiyotaka. She later attempted to recruit Kiyotaka into Class B by offering 20 million private points, emphasizing his perceived value in elevating the class. Her interactions with him include teasing and flirtatious remarks, such as suggesting she would have fallen for him had he been in her class or offering emotional comfort, though he typically remains indifferent. She displays a realistic, sometimes cynical outlook, openly admitting defeat in class advancement efforts while simultaneously vowing to obstruct Chabashira's class.