That the sister is interested in her foster brother's opinion is commendable. And assessing her worthiness from a man's point of view he can. But asking him to jerk off in front of her is kind of weird. He's going to get her, isn't he? Only this slutty girl is not scared at all - that's exactly what she wants. He ended up flushing a whole puddle on her tummy! Drove it.
That's what blondes are for: a place to rub your dick and a place to get high. And this bitch quickly learned her lesson and served her daddy. I see he was pleased when he came down in her mouth and let her lick the head. You bet he was!