In 'Death Note Another Note novel', a major theme is the search for truth. The characters are constantly trying to figure out who is using the Death Note and for what purposes. There is also the theme of the thin line between justice and vengeance. Some characters may think they are dispensing justice with the Death Note, but in reality, it might be more about personal vendettas. This blurry line is explored throughout the novel.
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.
Mello is quite an interesting character. His determination and his somewhat unorthodox methods make him stand out. He is willing to take risks and use his intelligence in creative ways to achieve his goals related to the Death Note.
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.
One of the main themes is the concept of justice. Light Yagami believes he is creating a new world of justice by using the Death Note to kill criminals, but his actions are morally ambiguous. Another theme is the power of knowledge. The power of the Death Note and how to use it effectively is based on understanding its rules.