Sae Chabashira is the homeroom teacher for Class D at Tokyo Metropolitan Advanced Nurturing High School. She appears as a young woman with long brown hair typically tied in a ponytail, brown eyes, and a well-endowed physique. Her standard attire includes a black blazer over a white polo shirt, paired with either a short black skirt and stockings or suit pants, completed with black or white heels. She occasionally wears practical outfits like tracksuits during exams and once donned a maid uniform for a school festival. She uses smoking as self-medication for stress relief. Personality-wise, she strictly enforces school rules and initially maintains detachment from Class D students. Her sadistic tendencies surface when announcing point shortages or threatening expulsion for academic failures, deriving enjoyment from student distress. Despite this, she shows rare leniency, such as accepting private points from Kiyotaka Ayanokōji and Suzune Horikita to prevent Ken Sudō's expulsion. She perceptively recognizes Kiyotaka's concealed intelligence and physical prowess. Her approach evolves from indifference to vested interest in Class D's advancement, motivated by regrets from her own student days. Her background reveals she attended the same high school in Class D years earlier. During a critical special exam, her refusal to nominate someone for expulsion caused her class to permanently drop rankings, resulting in lost friendships, a broken relationship, and failure to reach Class A. These regrets drove her to become a teacher. She sustains a complex friendship-rivalry with Class B's teacher Chie Hoshinomiya, rooted in shared history and conflicting class goals. Plot involvement begins with minimal intervention, ignoring rule violations and declining help against external threats like false expulsion accusations. After observing Kiyotaka's strategic abilities, she shifts tactics, fabricating expulsion threats from his father and demanding Class A promotion in exchange for protection. Kiyotaka exposes her lies about contacting his father, revealing she merely received instructions to monitor him as a special student. Post-exposure, overt coercion ceases though she continues monitoring his activities. Relationships center on instrumental dynamics. She views Kiyotaka primarily as a tool for class advancement, though their power balance shifts after her manipulation fails. With Suzune Horikita, interactions evolve from tactical use to mentorship, seeing parallels to her younger self. She demonstrates fleeting concern for students like Kanji Ike, reminded of her past boyfriend, but generally maintains professional distance from others. Character development shows gradual growth from detached observer to active supporter. Traumatic exams mirroring her student-era failures trigger emotional vulnerability, particularly witnessing Class D's collaborative decisions. After Class D ascends to Class A, she achieves her goal but exhibits subdued concern for displaced students. Kiyotaka's subsequent departure from the class causes visible distress, highlighting her deepened investment in student outcomes beyond initial ambitions.