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.