All of a sudden, Rachel's sister, Chloe felt a pressure in her bladder. "Are you sure, Rachel?", asked Chloe? But before Rachel could answer, Chloe began peeing into Rachel. Rachel felt herself "expanding" so much that she was filling to the brim. Rachel was in heaven. She couldn't believe how good it felt to be filling up with her sisters pee. As Chloe was still pissing into Rachel she noticed that she was full and starting to leak. Chloe then said "hey Rachel I think your leaking" Rachel decided on a wish to become a full sized diaper so she could hold more of her sisters piss. Rachel then said "I wish I was an extra puffy diaper" and before Chloe realized what happened her new diaper was pushing her legs apart and it was still growing. Chloe was in a slight shock because she had not stopped peeing and then she felt pressure in her stomach before she could say anything she was pushing out a sticky mess into her diaper sister. Rachel continued to grow from the mess being pushed and pissed into her. The new mixture caused Rachel to convulse in orgasm. Chloe then untaped Rachel and began massaging her pussy as Rachel's convulsions rubbed her clit. Chloe then began squirting into Rachel. After several orgasms, Chloe collapsed and sat back into her messy diaper. Rachel then said quietly, "I wish..."