Kami no gyakuten:The yamato hero - Chapter 20: The Illusion of Victory

The world that nurtured the civilization which reached the pinnacle of magic was on the verge of destruction.
The last survivor transmigrated to the past, when the magic civilization started growing, as countless mages were still fumbling their ways through the thorny paths of magic knowledge.
He, who came from the end of the magic era, aim to reach the pinnacle of magic.

- Description from Novelupdates

Kim Mu-ryeong is the youngest member of a famous exorcist family. He grew up receiving love from his entire family and was considered a genius. The kind that appears once every hundred years. “Mu-ryeong, let me make a request.” After enrolling in high school, Mu-ryeong began to do simple exorcism work. The apartment’s elevator is acting weird. Someone is having constant nightmares. Even things like getting rid of a stalker or acting as a boyfriend. It was more of a problem-solver job than exorcism, But Mu-ryeong, being someone who helped anybody, There was nothing he couldn’t accept. But even for Mu-ryeong, there was one person he avoided… “Ki Hwan-young?” Tall and handsome with a mysterious, intimidating aura, And known for being impolite and having no friends. One day, Ki Hwan-young came to see Mu-ryeong. “My shoulders feel heavy lately.”

When Su Jiu dies on her eighteenth birthday, she transmigrates into a novel about painful love and becomes an adorable four-year-old child.

Should an untalented guy like me die?Then I’m going to die.I will die as you so desire.After dying, I will challenge the world again.Until I kill this tr*sh-like world!