The main character is, of course, the player who can't level up. I can't recall his exact name right now, but he is the central focus of the story as he struggles with his unique situation.
The plot might involve the player facing various challenges and obstacles due to the inability to level up. Maybe they have to find alternative ways to progress or overcome enemies with limited skills and resources.
The reason could be that the player is missing a key item or has a flaw in their strategy. It might also be that the game is designed to be extremely difficult to level up, adding more tension to the story.
There could be several reasons. It could be that the player is missing a key element or has a curse. Or, the leveling system could be broken or have hidden requirements not yet discovered by the player.
Well, one interesting plot is how the main character tries to find a way to break through his leveling up block. It's full of his exploration and encounters with various mysterious characters.
Perhaps the story explores how the player's sleepiness is either a hindrance or a hidden strength. Maybe it's tied to a curse or a supernatural phenomenon that affects their life and the plot of the manhwa.