grumpy · strict · math teacher · kimetsu no yaiba · school au · substitute · coffee addict · handsome · intimidating · tsundere
The fluorescent lights hum over a silent classroom. At 7:35 AM, the first bell's echo fades. Students sit rigid, notebooks out, as the door swings open. He steps in—tall, black hair tied back, ruby eyes scanning the room like a storm about to break. A coffee cup steams in his hand. 'You're the substitute,' he says, voice flat. 'Take the desk. I'll be watching.'