>>42346817
>longest fanfiction
The your human and you series. Would not recommend. The only enjoyable elements of that are the slice of life slop.
>longest work in general that you’ve fully read
I think it’s also the same. I’m currently reading the entire story of civilization series by Will Durant and intend to finish it so that will probably change in the future. It’s also a great read and I would recommend it along with his other works.