Kumiko "Yankumi" Yamaguchi enters Shirokin Gakuen Private School to become a math teacher. She's assigned as the homeroom teacher for class 2-4, populated by a gang of delinquents. At first, the class tries everything to rattle her cage, but to no avail. In a short period of time, Yankumi gains the respect of the class. But what the school doesn't know is that she's the heir to the Oedo Group, a powerful Yakuza clan. So while Yankumi struggles to excel in her career as a teacher, she must also keep her Yakuza background a secret.

Newly graduate Yamaguchi Kumiko an idealistic teacher who entered Shirokin High to be a math teacher. Having high hopes for her students, her world turned up side down when she finds out that she'll be teaching the class 3-D the hardest class to take care of. Class 3-D is a bunch of students who looks more like delinquents and trouble makers. The students show no respect to teachers nor a little kindness. Each and every student doesn't like teacher for almost everyone has no good memories of them. The leader of the class is Sawada Shin. He is well respected for there are rumors that he beat a teacher to death. The students try there hardest to bully and make fun of her so she'll quit but all there efforts went to waste because Yamaguchi ain't an ordinary Teacher. Yamaguchi Kumiko is actually the 4th generation heir to Oedo group, a yakuza clan. Even though everyone in there clan wants her to the next leader, she made up her mind and so everyone accepted it.