Kumiko Yamaguchi aka Yankumi, oversees the new students of Class 3D of Akado High School. Her class is full of delinquents, but she tries her hardest to teach them not just about Mathematics, but about lessons of life. However, she's also the granddaughter of a Yakuza boss, Kuroda of the Kuroda Ikka, and is seen as the next in line to head the family business. However, her true passion lies in teaching. So she's forced to lead a double life and keep her family a secret from the public. Her Yakuza upbringing also happens to give her the strength and the experience to reach out to her students and at the same time provide many moments of comedic relief.
