The World Of This Fantasy Novel is in Crisis

“Not one person in this world is kind without a motive.”
“That’s not true. Some people are just kind with no reason at all.”

"I want to live the life of my sister's favorite character."
After losing his sister, OO is reincarnated into the world of her novel. Although he clearly expressed his desire to live the life of his sister’s most cherished character, how the hell did he become the villain, “Satin,” who dies in the first scene?
Determined to not to ruin his sister’s novel and faithfully play the villain, Satin, something still feels off. Unable to bear the role of the villain, Satin gives in and devises a plan to escape the protagonist, Cain. However, in the process of escaping, in the end, he parts ways with Cain and loses all his memories after his reincarnation due to amnesia.
Four years passed, and eventually Satin meets Cain once again, but yet his gaze seems strange again.
Why… Why does he keep looking at me like that? Why is he crying? Satin feels awkward seeing Cain like that.
"I thought you were dead. I really thought you were dead, so I wanted to kill everyone...!"
But what’s the point of killing…?
Characters:

Cain (Top):
A twisted hero who despises the world even after being saved by Satin, is consumed by misanthropy. He believes it’s okay for everyone to die, except Satin.

Satin (Bottom):
A commoner who wants to be a good person, believes in protecting children and the elderly but also understands the need to discern, when to intervene and when not to, therefore he won’t act recklessly.