Sure, Oregairu has a manga. The manga expands on the story and characters from the original source material. It offers a different perspective and more detailed plotlines.
One interesting fanfiction could be where they go on an adventure together. Maybe they explore an old, mysterious part of the town that holds some secrets from the past. They could encounter various challenges along the way and help each other out, deepening their bond in the process.
One idea could be exploring the origin of the Totsuka Blade in the Naruto universe more deeply. Maybe it was created by an ancient clan with a special connection to the afterlife. Another idea is to have a character other than Itachi use the blade in a completely different way, like a young ninja who discovers its power accidentally.
Character growth is also a big theme. Characters from both series might face new challenges in the crossover setting of the fanfic. For example, a character from 'Naruto' might have to deal with the complex social hierarchies in 'Oregairu' high school, which would lead to their growth in understanding different social dynamics. Similarly, characters from 'Oregairu' could learn about determination and loyalty from 'Naruto' characters.
It depends on personal preference. If you like visual and auditory experiences, the anime might be better for you. The anime has great voice acting and animation that can bring the story to life. For example, the expressions of the characters and the background music can enhance the emotional impact. However, if you enjoy in - depth reading and exploring every detail of the story, the light novel is the way to go. It can offer more complex character thoughts and additional plotlines.
Overall, the OreGairu manga follows the light novel pretty well. There might be some minor differences in the way certain scenes are depicted or the emphasis on certain details, but the core story remains intact.