Godammit, gachinkou. Fatguy again? WTF is up with this author's fascination for hairy, ugly fat old men? Brrr. Even Rider's uber sexiness isn't quite enough to make up for his presence...
Don't see how this is NTR. Rider is not an option, no matter how much the fanboys want her to be, she's not. There's a few tryst involving Sakura and Shirou in Fate/Hollow (which is not canon, even if you consider Sakura's route to be as "canon" as Saber's) but that's to appease the Rider fanboys more than anything.