I was the op who asked whether to watch Bakemonogatari a few days ago.
Just watched Nisemonogatari Episode 8.
Did he just fuck his sister at the end , right after the episode he fucked crab?
It's strongly implied
But you can't believe a word Araragi says.
Nise is one of the better gataris you scum. Aside from Kaiki, and Kaka, a lot of the plot was great. Admittedly bee arc was a little weak, but bird was actually great, the finale was sick, and some of the dialogue was amazing. The bathtub scene was great, the courage to tell a lie was amazing, and the toothbrush will forever be remembered, which makes it great.