Yamaguchi Prefecture is situated in the west of the Japanese island of Honshu.
Occupying an area of 6,108 square kilometers, Yamaguchi is bordered by the Sea of Japan, the Inland Sea, and the Hibiki Sea and by Shimane and Hiroshima prefectures.
The capital is the city of Yamaguchi located in the center of the prefecture.
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.
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.
The teacher Yamaguchi Kumiko, later nick named Yankumi by her students had her secret connection to the Yakuza family, and that was used to give her uncontrolled outburst of Yakuza vocabulary which was very funny.