Kana Kojima is a 23-year-old Japanese language teacher at Kawanuma West High School, initially feared by students and delinquents as "Kojima the Demon" or "Ogre Kojima" due to her strict demeanor. This imposing reputation starkly contrasts with her private clumsiness and frequent entanglement in accidental erotic situations, particularly involving student Ichiro Sato. Physically, she possesses dark brown hair typically tied up with a red hairband, amber eyes, and fair skin. She stands 159 cm tall with measurements of 89-57-86 cm, her large bust and wide hips often concealed by conservative teaching attire: a white blouse, dark blue skirt, dark brown thigh-high stockings, and black pumps. As a high school student, she wore red-rimmed glasses and a sailor-style uniform with a red neckerchief. Her personality combines stern professionalism with deep-seated shyness and insecurity rooted in an extremely reserved and confidence-lacking adolescence. A pivotal event occurred at age 17 when she rescued 11-year-old Ichiro Sato from a river; his belief that their shared bravery made them "adults" profoundly inspired her teaching philosophy. This led her to adopt a courageous, intensive approach, though she remains emotionally vulnerable—afraid of thunder, easily flustered in intimate situations, and possessing a comically poor grasp of sexual matters, such as believing pregnancy could result from swallowing semen or requiring Sato to explain condoms. Her relationship with Ichiro Sato evolves from repeated accidental encounters in places like bathrooms, laundromats, pools, and beaches into secret dating while he is her student, continuing after his graduation. She values his kindness, youth, and affinity with children—traits matching her partner criteria. Post-graduation, they live together with her surname on his apartment nameplate, acting as fiancés. She grows close to his family, especially his mother Saki, a childhood friend, and desires motherhood, practicing childcare with Sato's sister Shio. Throughout her development, she maintains her "demon" persona professionally but gradually reveals more vulnerability and affection toward Sato, transitioning from tsundere-like behavior to openly relying on him. Her cooking skills and helpful nature are noted, alongside her consistent inability to tolerate alcohol—becoming clingy and intoxicated after one sip. By the manga's later volumes, she balances teaching ferocity with private domesticity, progressing toward marriage with Sato while navigating comedic misunderstandings about relationships and sexuality.