The Legend of Sun Knight - Volume 5, Chapter The First Misdeed of an Undying Lich: “Frightening Children into Being too Scared to Sleep at Night” — translated by bleachpanda

The leader of the thousand demons, the Demon God Chun YeoWoon. Due to an unfortunate accident, he had been sent to the distant future.

Childhood sweethearts.
The most popular person in school is my childhood sweetheart.

- Description from Novelupdates

A man who was once called the world’s strongest agent ended up becoming a teacher after his retirement, to train a new generation of agents. After many years of training his disciples, he was killed at the age of 60 by a secret organization’s ruse and was reincarnated in another world with his memories intact. Though he was surprised by the existence of magic and the strange species in that world, he quickly adapted to his condition as a newborn and took advantage of it. He acquired special magic and gained a massive amount of strength thanks to his rigorous discipline, in order to reach his goal: Resume his career as a teacher which he left halfway through in his previous life. This is the story of a man, who, based on the memories and the experiences of his previous life, became a teacher who travels through the world with his students.

“Only by enduring 2¹⁴ trials can one awaken the ancient power sleeping within the Key of the Star Prison, and become the most powerful being in the universe.”Timothy, the youngest Demon Lord in the history of his race, saw these words emerge after he touched the Key of the Star Prison, the most powerful artifact of the demon race, handed to him just before the old Demon Lord's death.According to the demon race's records, no Demon Lord had ever achieved this.However, over a span of a hundred thousand years, Timothy had easily passed 16,383 trials.Now, once again, he turned the Key of the Star Prison, and an unknown force mistakenly sent him to a brand new world, transforming him into an unknown and seemingly worthless demonic cultivator disciple.And the formidable opponent he was about to face in this world was the powerful Goddess Sylvia.When Goddess Sylvia received the challenge Timothy handed her, her cheeks flushed...“My dear Sylvia, I want you to know how deeply I love you. My heart belongs to you, now and forever.”