Transmigrated as the Novel's Final Boss

“How many people have you killed? How many families have you destroyed? How many towns and cities have fallen because of you!?” “I don't remember.” The villain whom the main character was destined to defeat at the end of the novel. That was who I had become. There was just one problem... “Why am I a teenager!?” “Why is there a school acceptance letter on my desk!?” — Description from novelcodex.org