Sex with his girlfriend has been in a rut lately.

She happens to find an NTR manga on her boyfriend's bookshelf.
She decides to find a playboy and record their NTR (netorase) play.

She feels guilty, but she can't resist the pleasure as she is overwhelmed by the stranger's technique and his big cock.
"What's this feeling... It's totally different from my boyfriend..."

He feels frustrated but excited by the sense of inferiority as his beloved girlfriend is fucked by another man on the other side of the screen.

(Source: Fanza, translated)