You could check at your local bookstore. Some larger chains or independent stores that carry manga might have Naruto box sets. Another option is to search on manga-specific websites or forums where collectors might be selling or recommending places to buy.
It depends. If you're a big manga fan and love having a collection, they can be totally worth it. You get multiple volumes in one go and can enjoy the series without having to hunt for individual issues.
It's possible for manga box sets to be fake. Sometimes, poor-quality reproductions are made and sold as the real thing. This can be difficult to spot for the average buyer.
Sure. The characters are a huge part of Naruto Shippuden fanfiction. Fanfic writers use the characters to attract readers who are fans of those characters. They might focus on a character's backstory that wasn't fully explored in the anime and expand on it. Also, the interactions between characters in the original show give fanfic writers ideas for different scenarios in their stories.
By their unique abilities. Naruto's Rasengan, Sasuke's Sharingan, these abilities can be the starting point for many fanfiction ideas. Writers can think about how these abilities could be used in different battles or situations not shown in the original.
One of the most popular is 'Naruto Shippuden: Sakura Hiden - Thoughts of Love, Riding Upon a Spring Breeze'. It's popular because it shows Sakura in a new light, with her own adventures and growth.
Manga box sets are expensive because they include multiple volumes in one package. This saves you from buying each volume separately, but the combined cost along with packaging and distribution expenses adds up.
I don't think it's strange at all. Naruto is a very curious person. Fanfiction can offer new perspectives on his own life and the lives of his friends. He might learn something new about himself or get inspired by the creative ideas in the fanfiction. It could also be a form of entertainment for him during his downtime.