A major theme is growth. Naruto, being a character known for his development in the original series, continues to grow in these fanfictions, and Isane also experiences personal growth as she interacts with Naruto. Additionally, the theme of cultural exchange is common. They come from different backgrounds, and the fanfictions often show how they share and learn from each other's cultures. For example, Naruto might teach Isane about his ninja way, while Isane could introduce Naruto to her world's medical practices if she is a medical - related character. It makes for an interesting dynamic as they both evolve through these exchanges.
One popular 'naruto x isane fanfiction' might be 'The Unlikely Bond'. It often shows Naruto's adventures in a new world where he meets Isane and they develop a unique friendship that gradually turns into something more. It has interesting character interactions and some exciting plot twists.
In my opinion, both have their merits. The anime brings the characters to life with animation and sound, but the manga allows for more imagination and detail in the panels. It really comes down to what you value more in your entertainment.
Bleach is not a novel. It's more famous for its manga and anime versions. The manga format allows for a more visually dynamic and action-packed presentation of the story compared to a traditional novel.
Rukia would probably be very critical at first. Since she is quite serious, she might nitpick the inaccuracies in the fanfiction. But she might also secretly enjoy the ones that show her in a positive light, like those highlighting her friendship with Ichigo. In the Bleach universe, characters are used to their own stories, and fanfiction would be a whole new and unexpected take on their lives. The zanpakuto spirits might also have interesting reactions if they could read, as they have their own personalities and might be offended or flattered by how they are depicted in the fanfictions.