Kumiko (known by her students as "Yankumi") becomes a teacher at an all-boys private high school. Her class is full of delinquents, but she tries her hardest to teach them not just about academics (her subject is Mathematics), but about lessons of life, much like any "dedicated teacher" story. Though she's forced to keep her family a secret from the public, her Yakuza upbringing gives her the strength and the experience to reach out to her students, while also providing comedic relief.

Cast
* Nakama Yukie as Yamaguchi Kumiko (Yankumi / Ojou / Kumichou) (Math Teacher/Class 3D adviser)
* Matsumoto Jun as Sawada Shin
* Namase Katsuhisa as Sawatari Goro, Kyoto (School Vice Principal)
* Utsui Ken as Kuroda Ryuichiro (Kumiko's grandpa / 3rd Generation Oedo Yakuza Boss)
* Anan Kenji as Wakamatsu Hiro
* Kaneko Ken as Asakura Tetsu
* Uchiyama Shinji as Tatsukawa Minoru
* Ryogoku Hiroshi as Sugawara Makoto
* Oguri Shun as "Uchi" / Uchiyama Haruhiko
* Waki Tomohiro as "Kuma" / Kumai Teruo
* Narimiya Hiroki as Noda Takeshi
* Ishigaki Yuma as Minami Youichi
* Ito Misaki as Fujiyama Shizuka (English Teacher)
* Nakazawa Yuko as Kawashima Kikuno (School Nurse)
* Nabe Osami as Ando Osamu (Social Studies Teacher)
* Kohmoto Masahiro as Iwamoto Kouhei (P.E. Teacher)
* Okuma Ichiro as Oyama Hajime (Science Teacher)
* Tayama Ryosei as Shirakawa Gonzou (Principal)
* Saito Satoru as Washio Kanji (Japanese Language Teacher)
* Sawamura Ikki as Shinohara Tomoya (Police Officer)
* Sakata Tadashi as Kashiwagi Yutaka (Police Officer)