Kumiko Yamaguchi: 23 years old. A mathematics teacher at Shirokin Gakuin High School and the homeroom teacher for Class 3-D. Commonly known as "Yankumi." She works as a teacher while hiding the fact that she is the fourth-generation heiress to the yakuza syndicate "Oedo Family."

Shin Sawada: 17 years old. A student in Class 3-D. He is highly intelligent and deeply trusted by his peers. While he has a faint suspicion about Yankumi's true identity, he places his trust in her.

Haruhiko Uchiyama: 17 years old. Nicknamed "Uchi." One of the central figures in the delinquent group.

Yoichi Minami: 17 years old. A student in Class 3-D who is short-tempered but cares deeply for his friends.

Takeshi Noda: 17 years old. A student with a stylish and lighthearted personality.

Teruo Kumai: 17 years old. Nicknamed "Kuma." His family runs a ramen shop. He has a large build and looks up to Yankumi.

Goro Sawatari: 45 years old. The Vice Principal of Shirokin Gakuin High School. He views the problematic Class 3-D and Yankumi as enemies and is constantly in conflict with them.