The story of a young, idealistic teacher who enters Shirokin Gakuen with hopes of making a difference in the students' lives. However, Yamaguchi Kumiko (Nakama Yukie) is in for a rude awakening when she finds that she will be the homeroom teacher of 3-D, the hardest class to maintain in the school. The students have multi-colored hair, sloppy uniforms, and show absolutely no respect to her. The leader of the class, Sawada Shin is lazy but bright and shows some interest in Yamaguchi when he notices that she is very different from other teachers. The students try to bully her to make her quit, but their attempts don't get them very far.

What the class and the rest of the school does not know is that Yamaguchi Kumiko is actually the 4th generation heir to the Ooedo Group, a notorious yakuza clan. Even though her family would like her to take the title of Ojou when her grandfather dies, they have accepted the fact that Yamaguchi would rather be a teacher.

Eventually, the students learn to respect their quirky teacher because of her devotion to them, and even give her a nickname: Yankumi.


Cast
* Nakama Yukie as Yamaguchi Kumiko (Yankumi / Ojou / Kumicho) (Math Teacher/Class 3D adviser)
* Namase Katsuhisa as Sawatari Goro, Kyoto (School Vice Principal)
* Enami Kyoko as Akagi Ryoko (Board Chairman)
* 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
* Takaki Yuya as Ogata Yamato
* Miura Haruma as Kazama Ren
* Ishiguro Hideo as Honjo Kengo
* Nakama Junta as Ichimura Rikiya
* Kiriyama Akito as Kuraki Satoru
* Miura Shohei as Kamiya Shunsuke
* Waki Tomohiro as "Kuma" / Kumai Teruo (Former student of Yankumi)
* Azuma Mikihisa as Baba Masayoshi (PE Teacher)
* Koizumi Kotaro as Natsume Seichi (School Doctor)
* Hirayama Aya as Takano Aoi (English Teacher)
* Hoshino Aki as Ayukawa Sakura (School Nurse)
* Sato Jiro as Yajima Hosaku (Japanese Classics Teacher)
* Sakigake Santaro as Hatoyama Yasuhiko (World History Teacher)
* Ishii Kota as Tsuruoka Keisuke (Physics Teacher)
* Ishihara Atsumi as Kumai Ami (Kumai Teruo's wife)
* Yamada Yu as Kazama Kaoruko (Kazama Ren's sister)