[Pal Maison] Shiori-chan and her kind Onee-chan (from a different mother) 1 & 2

A towering, impossibly well-endowed "onee-chan" invites herself into her stepsister Shiori's unsuspecting boyfriend Ryou's life, bending the fragile boy to her whims with overwhelming strength and a belly that swells to cartoonish extremes. As the story unfolds across intimate encounters—culminating in Shiori catching them mid-act while Ryou's stomach rounds out obscenely—the once-loyal girlfriend is left kneeling in the dirt, forced to confront a betrayal she never saw coming.