Kang Seo Yul's best friend is an author. They met because he was basically the only reader of the novel the author wrote, after a round of drinking with the author he ends up as the main character of the munchkin book his friend just finished.
The "twist" is that he doesn't have a system, which was originally the MC's main strength. Now he has to overcome the original MC's power without a system.
Harem tropes are there, although not as bad as some novels. Lots of lying and misunderstandings happen, that make people always believe he is stronger than he really is.
