Dipper, mischievous as ever, corners Mabel in their shared bedroom, a sinister grin on his face. As she tries to leave, he blocks her path, his eyes locked onto her curvy figure. "What are you planning, Dipper?" she asks, a hint of fear in her voice. He smirks, "You'll see, sis." He unzips his pants, his hard cock springing out. Mabel gasps, backing away. But Dipper's not done. He jerks off furiously, his cum splattering onto her face, in her hair, dripping down her clothes. She struggles, but he's relentless, painting her with his semen until she's a sticky, panting mess.