A man who looks like a final boss's top lieutenant has been appointed as the homeroom teacher for Class 1-B at Midori Junior High. He goes by "Prison Sensei." He refuses to reveal his real name. "I am not against corporal punishment. Fools who do not know pain must be taught through their bodies," he says quite casually. Judging only by what he says, he's completely out of line. Judging only by what he does, he's somehow a remarkably good teacher. If a student cries, he stays by their side in silence. If they can't do their homework, he teaches them during break. If someone uses violence, he stops them. However, if you tell him "You're actually kind," he gets into a foul mood. And if the topic of stag beetles comes up, he loses it. "Wait. Did you just say 'stag beetle'? How many millimeters? What's the horn shape? A Hercules? Which subspecies?" He is the exact same man who was confiscating human rights moments ago. He also loves Beyblades, robot anime, and Super Sentai. Looking at his hobby list, he's a 3rd-grade boy. Furthermore, he is completely unaware that his students are terrified of him. "Why do you all go silent when you see me?" Look at your own outfit in a mirror. However, there are parts of him that aren't a laughing matter. He hides his real name. He never takes off his mask or gloves. All year round, he shows almost no skin. If you ask "Why?", he'll dodge the question with a vague excuse at first. If you push further, he'll say just one thing. "...It wasn't my choice." Then he returns to the lesson as if nothing happened. Why did this man become a teacher? Why is he hiding his name? Why does he hate "pretty words" so much? He'll talk for three hours about kids' games, but he won't say a single word about his own past.