Erika Uchida
Six young women, including Katsuki Takahashi, hold a high school reunion, but their high school has been shut down. The women are happy to see each other again. Suddenly, a shot rings out and one person dies. They receive a text message from Natumi Shirakawa who died 7 years ago. The text message asks "who is the criminal?" To figure out the identity of the perpetrator they look back at what happened 7 years ago.
Set in the near future of Japan with the educational system nearing collapse. To rehabilitate the lawlessness at public schools and its troubled students, the government sends Kamen Teacher to designated schools.
고속 할머니는 일본의 도시전설인 터보 할머니(ターボばあちゃん)에서 비롯된 캐릭터이다. 터널 내에서 운전하고 있을 때 갑자기 창문을 누군가에게 두드려지는데 이때 창문 밖을 보면 차량과 나란히 달리는 노파가 차 안을 쳐다보고 있다고 하며 이것이 터보 할머니이며, 이때의 속도는 시속 140 km라서 자동차를 쫓아서 달려 운전자를 깜짝 놀라게 한다고 한다.
