Nanako Mizuki is a student from a wealthy family who first appears as one of Eikichi Onizuka's earliest and most significant challenges when he begins teaching. She comes from a privileged background but lives in a deeply troubled home environment, where her relationship with her parents has become strained to the point of breakdown. This family deterioration leaves her feeling isolated and disconnected, and she initially expresses this pain through rebellious and deceitful behavior. Shortly after Onizuka's arrival, she lures him into a trap together with two male friends in an attempt to extort money from him, but her plan fails because Onizuka does not fall for it. Beyond the scheme, she is genuinely searching for someone to trust and connect with, and she sees in Onizuka a potential figure who could fill the emotional void left by her family. Her personality is a blend of vulnerability and defiance; she is willing to act out in harmful ways because she feels abandoned, yet she also longs for understanding and support. Onizuka eventually reaches her by confronting the source of her pain in a dramatic and physical manner, destroying part of a wall that symbolizes the emotional distance she feels from her family. This act breaks through her defenses and leads to a significant change in her attitude. She comes to admire Onizuka deeply, developing a strong attachment to him and even expressing a romantic interest, declaring that she will wait for him when he becomes the greatest teacher in Tokyo. Within the story, she plays the role of an early test of Onizuka's unconventional methods, demonstrating how his willingness to engage with students on a personal and even physical level can reach those whom traditional approaches have failed. Her key relationship is with Onizuka himself, whom she affectionately calls Onichi, and she becomes one of his most loyal and supportive allies after their initial confrontation. She also has two male friends who are part of her early schemes, and together they side with Onizuka after he wins them over. Her development is marked by a shift from manipulative and distrustful behavior to openness and loyalty, as she learns to place her trust in someone who genuinely cares about her well-being. She does not possess any extraordinary physical or intellectual abilities; her notable strength lies in her capacity to change once given a reason to believe in others, and her role in the narrative highlights the importance of addressing the root causes of student misbehavior rather than simply punishing it.