The JJBA manga is indeed finished. It had a great journey and wrapped up with a satisfying conclusion for fans. However, there's always the possibility of spin-offs or related works in the future.
The contrast between their personalities. Jotaro is the cool and stoic type, while Josuke is more hot - headed and energetic. This creates an interesting dynamic in fanfictions. Their shared connection within the JoJo universe also adds to the appeal. Writers can explore their relationship in different ways, whether it's a friendship that develops into something more or a deep bond from the start.
You can start by looking on popular fanfiction websites like Archive of Our Own (AO3). There are often tags and filters you can use to specifically search for Jotaro x Josuke fanfictions. Another option is Fanfiction.net, which also has a large collection. You might also check out Tumblr, where fans sometimes share and recommend their favorite fanfictions in this pairing.
There's also 'Diamond in the Rough'. This fanfic focuses on a unique relationship between the reader and a JJBA character. The writing style is very descriptive, especially when it comes to the Stand battles. It really brings the action to life and makes you feel like you're in the middle of the chaos.
Some JJBA fanfics that are worth reading are the ones that expand on the battles. They might add more complex strategies or new foes that the characters have to face. For instance, a fanfic could introduce a new stand user who has the power to manipulate time in a different way than Dio. Also, fanfics that give a different perspective on the existing story arcs, like seeing the events of Stardust Crusaders from an enemy's point of view, can be quite engaging.