In fact, the manga of Death Note has its unique ending that sets it apart. It's a conclusion crafted specifically for the original comic format, with elements and developments not found in other versions.
Yes, I recommend the novel "I, the Grim Reaper, Have Billions of Believers." It was a light novel, a derivative doujinshi novel. The plot was very exciting. The main character had hundreds of millions of believers and gathered the power of hundreds of millions of believers. In addition, this novel had been completed. It was a long novel with a million words and was very worth reading. I hope you like this fairy's recommendation. Muah ~😗
Ryuk would probably just be amused. He is a Shinigami who has seen a lot in his existence. Fanfiction is just another strange human creation to him. He might chuckle at some of the more outlandish ideas in the fanfictions, like a character having superpowers beyond the Death Note.
Misa would likely be excited. She is a big fan of Light and the whole 'Kira' concept. In fanfiction, if there are scenarios where she has more power or a closer relationship with Light, she would be all for it. However, she might also get jealous if there are other female characters getting too close to Light in the fanfictions.