Well, some characters might be flattered by the fanfiction. For example, the main character in Solo Leveling could be amused to see different interpretations of his adventures. He might think it's cool that fans are so creative with his story.
The main character, Sung Jin - Woo, is surely an important one. He has been the central figure throughout the series, and in the 128th novel, he'll probably continue to be the key player.
The Solo Leveling manga has a considerable number of chapters. But the exact length can vary depending on how you measure it, like in terms of page count or story arcs.