In the early 1990s in the Shonan region of Japan, before he would ever become a legendary teacher, Eikichi Onizuka and his best friend Ryuji Danma are the infamous Oni-Baku, or Demon Explosion, the most feared duo in the local biker gang scene. Known for their tenacity in a fight, their reputation as violent delinquents proceeds them wherever they go, which presents them with their greatest problem: their fearsome image terrifies the opposite sex, and the two remain desperate to lose their virginity and find romance. Determined to turn over a new leaf, they attempt to leave their gang lifestyle behind, a goal that proves easier said than done.

After faking their expulsion from their previous school, Onizuka and Ryuji enroll at Tsujido High School, hoping for a fresh start. Their summer plans to meet women at a resort on Yoronshima Island end in disaster when the two college students they charm turn out to be their new homeroom teachers, Mariko Izumo and Ayumi Murakoshi. The revelation creates an awkward dynamic, especially as Ryuji begins developing genuine romantic feelings for the earnest Ayumi. Despite their efforts to lay low, their fighting skills quickly draw attention when they defend the school from a rival gang, instantly cementing their feared reputation all over again.

The series chronicles the duo’s daily battles and misadventures as they clash with a colorful gallery of rivals and allies. They encounter Toshiyuki Saejima and Jun Kamata, the brutal Kamakura Mad Dogs who terrorize anyone who mentions the Oni-Baku name. After a brutal confrontation, these enemies eventually become grudging followers. They befriend the smooth-talking womanizer Hiroshi Abe, who teaches them that the secret to success with women is money, and gather a loyal entourage of schoolmates including the awestruck Makoto Hashiri and the hot-headed Tsuyoshi Tsukai.

A major narrative arc involves the arrival of a new sadistic guidance counselor, Yoko Minamino, whose draconian rules and brutal corporal punishment push the students to their limits, leading to a decisive showdown with the Oni-Baku. The peace is further threatened by the rise of a powerful new gang led by the wealthy and ruthless Fumiya Shindoji, who systematically attacks other delinquents and kidnaps Ayumi, forcing Onizuka and Ryuji into a desperate rescue mission. The live-action adaptation also mixes in storylines such as Onizuka being tricked into a potential marriage with a young mother named Aina Yarita and the appearance of a girl named Nagisa Nagase, whose traumatic past has created a violent split personality called Yasha that targets Ryuji. As the series progresses, the Oni-Baku must navigate the fine line between their loyalty to their friends, their desire for maturity, and the chaotic legacy of their violent youth.