It might be the unique plot. Maybe it takes the RWBY characters and puts them in situations that are different from the original series but still in - line with the overall RWBY universe.
I'm not sure of specific fanfics similar to it off the top of my head. But you could try searching on RWBY - dedicated fanfic websites like Archive of Our Own. There are likely to be fanfics with similar themes or tones.
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.
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.
I'm not sure specifically as I haven't read it. It could be a story about love that has some sort of 'biting' element in a metaphorical sense, like a passionate or intense love.