Nanako Mizuki is a high-school student at Musashino Public High School. She is the first troubled student that Onizuka helps on his path to greatness.
Nanako's family used to live in a six-tatami apartment, but were very close to one another. Both her parents worked hard to provide for the family and eventually both became very successful, with her father owning a food franchise and her mother owning four stores and importing goods. The increase in wealth lets the family move into a much larger house, but afterwards her parents become so wrapped up in their work that they hardly talk to each other anymore.
Shortly after Onizuka becomes Class O's teacher-in-training, she aids some of her fellow students in a blackmail scheme against their new teacher. She lures Onizuka her back to his apartment where she quickly strips and her co-conspirators take a photograph and threaten to leak it to the tabloids.
The plot is foiled by Onizuka with is own special brand of persuasion. Despite being set-up previously, he still agrees later on to give Nanako a ride back to her house after being promised her panties. The two eventually end up back at his place where she tells Onizuka how the small apartment reminds her of a happier time when her family was much closer, and there weren't walls between them.
Onizuka's solution to Nanako's problem is to stroll into her home with a sledgehammer, and bash a hole in the wall separating her parents' bedrooms. Her parents have the physical hole filled, but she realizes that time and her efforts can mend the family and make it whole again. To show her appreciation, she briefly, and without panties, flashes for Onizuka.