Yamaguchi Kumiko, age 23 and fresh out of college, obtains her first teaching position as a math teacher in Shiroken High School. The school itself has a pretty bad reputation, and to make it worse, Kumiko gets saddled with the most ill-mannered students in the school – class 2-D (3-D in the drama). Slowly, she earns their respect as she helps them with their problems and proves that she really cares for them time and time again. However, Kumiko is harboring a secret: she is from a yakuza (Japanese mafia) family and is heiress to the Ooedo Clan. If anyone were to find out, her dream of being a teacher would be over!