Textbook of Revenge

Ryoutarou Kurose dreams of becoming a teacher, looks up to his homeroom teacher Shiratori-sensei and is subject to gruesome bullying. One day, fearing their actions have been exposed the bullies tell Kurose on the rooftop, "Before we get found out, why don't you kill yourself?" Terrified of what was happening Kurose loses his footing in the commotion and falls... "Hey, teacher. Can I do this over again?"

(Source: Publisher, translated)