In Death Note fanfiction, Ryuk and Rem have a rather complex relationship. Ryuk is more of an indifferent observer of the human world, while Rem has a deep emotional investment in Misa. Their interactions can be really interesting. Sometimes they might cross paths in the Shinigami realm or in relation to the actions of their respective human owners. Ryuk might find Rem's loyalty to Misa strange given his own non -chalant attitude towards Light. It's these differences that can create some really engaging scenarios in fanfiction.
In 'Death Note Ryuk x Rem Fanfiction', a frequent theme is the contrast between their loyalties. Ryuk doesn't really have a strong loyalty to Light, he's just entertained by him. But Rem is extremely loyal to Misa. This contrast often leads to interesting scenarios where they either clash or come to some sort of understanding. Also, the theme of their different views on the power of the Death Note is common. Ryuk sees it as a source of amusement, while Rem is more cautious about its use due to her love for Misa.
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.
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.