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.
Naruto would first be extremely confused by the rules of the Death Note. His understanding of power and its consequences is rooted in his ninja training and his own moral compass. The Death Note's rules, which seem so simple yet so deadly, would be completely foreign to him. He would question why anyone would create such a thing and would be very hesitant to even consider using it, as it goes against everything he stands for in his world of ninjas, friendship, and protecting the innocent.
The shinobi world's reaction would be complex. At first, there would be disbelief. Many would think it's some kind of new genjutsu or a hoax. But once they realize it's real, the more superstitious ninja would see it as a curse from the gods. The Hidden Sand Village might see it as a potential weapon against their enemies, while the Hidden Mist Village might be more cautious due to their history of bloodshed. The shinobi academies would start teaching about the Death Note as a new and dangerous threat. There would also be a black market for Death Note information, with some trying to sell false ways to protect against it.
Harry would likely be very conflicted. He has seen a lot of death and has always fought against dark magic. The Death Note's power to kill just by writing a name is something that goes against his values. He would probably try to keep it away from others and might even consider destroying it.
It focuses on the story of L's early days and how he solves cases. In this novel, we see L's unique detective methods and his battle of wits against various criminals.
Yagami was the protagonist of the Japanese suspense manga Death Note. He was the son of the police chief, Night God Soichiro, and came from a wealthy family. In the manga, Yagami was portrayed as a perfectionist with a beautiful appearance, all-rounded sports, excellent acting skills, and strong psychological quality. He had superior intelligence and malice, and was considered a perverted criminal. Night God Moon's abilities included an excellent mind and a stable mind. He could design a plan to drive a wedge between the police and the enemy, and he could remain calm while processing a large amount of information. He pursued a new world without crime, believing that the world was decaying. Night Goddess Moon's personality and fate were deeply explored in the Death Note. He was a well-loved character because he represented the possibility of indulgence, but he also experienced many failures.
Ron might be a bit more conflicted. On one hand, he would understand the need to get rid of really bad people. But on the other hand, he would be put off by the cold - blooded nature of Light's actions. He would probably say something like 'There's got to be a better way than just killing them off without a second thought.'
Characters like Near might analyze the fanfiction. He'd probably look at the logic behind the plotlines in the fan - made stories and compare them to the real events in the Death Note world. If the fanfiction has a really convoluted and illogical plot, he might dismiss it as being not worthy of his attention. But if it has an interesting take on the characters' motives, he might give it more thought.