Slow Prison Life - Chapter 36 - Monkey Goes For a Walk in the Royal Palace

I exist in the darkness, disappear under the bright light, and will eventually devour the sun and turn into the shadow of all things… Known by people as the indescribable terror of darkness; the king of shadows; the dark day; the existence of the shadow of the world , is still just a somewhat special high school student, facing a weird death game…

- Description from novelbuddy

Upon meeting the girl who would become her adopted younger sister, the duke’s daughter Christina regained memories of her previous life. Through those memories, she learned that her new sister, Mishuli, was the heroine of a certain story. And though the story depicted a Christina who abused her sister, the real Christina turned into a siscon who spoiled Mishuli to no end.

The unparalleled Demon King Ye Xuan, who was able to heal the death or the living alike and holder of the medicine Holy Scripture, was betrayed and killed by his fellow Demon Kings. But he reincarnated into the body of Ye Xuan, the prodigal son of the Ye family and vowed to himself that he would return to his peak and take back everything that belonged to him!

- Description from Novelupdates

The story begins with the last day of Yggdrasil, a popular online game which is being quietly shut down. Our protagonist Momonga decides to stay in his beloved game until the last moment, so waits for the forced logout. Unexpectedly, the server does not shut down and Momonga is stuck in a skeleton avatar in another world. “The powerful Overlord” needs now to discover the new world and face the continuous challenges that arise.