The Devil's Isekai

"I... will kill everyone who made me suffer, I will torture them till the end of time and turn their lives into a living hell." Shuku Ryuu is a Japanese high school student, he was bullied badly in school, from day to night the bullies wouldn't let him live peacefully without doing many terrible things just to satisfy themselves. But after a long time of being bullied, he accepted his fate to be their toy, willing to be used as a sandbag as long as he can endure. Only after he and his classmates got teleported to a fantasy world where magic existed, he thought he would be free from the bullies in this new world. However, the bullies wouldn't set him free, they set him up and his classmates betrayed him, and Shuku is then sold as a slave by his own classmates. Despite being summoned to this world by the Royal King as anticipated heroes who would defeat the Forces of the Demon Lord and save the world. But he didn't care, all he wanted was for his bullies and enemies to know his pain, he bowed to make every single one of them suffer in agony even if he had to die. And he will get his revenge.