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.
There could be a fanfic that focuses on Luigi's training to control his death stare. He might seek out the help of a wise old Toad who has knowledge of ancient powers. This would make for an interesting story as Luigi tries to master this power without causing harm to his friends.
It often shows the fragility of life. For example, in many post - apocalyptic sci - fi stories, characters are constantly facing threats that could end their lives. This makes the reader or viewer acutely aware of mortality.
Oh, for sure! Death Note is considered a masterpiece in the manga world. Its unique concept and the way it unfolds make it a must-read. The characters' development and the moral dilemmas presented make it stand out from the crowd.