But...

John drank in the sight of Sarah's exposed breasts. "They're perfect," he said, his voice barely above a whisper. He reached out and grabbed them again, feeling her warm titflesh in his hands, the points of her straining nipples pressing into his palms. He gave them a squeeze and a heft, excited at how how soft and firm his sister's orbs felt. "The only way they could be better is if...if they were just a little bigger."

As soon as the words left John's mouth, he felt a strange tingling in his hands where they rested on Sarah's chest. To his utter astonishment, her B-cup breasts began to grow and swell, expanding rapidly, pushing his hands away from her body as the volume of soft but firm flesh under them increase, the hard points of her nipples leading the way. Sarah gasped, arching into John's hands as her breasts enlarged, biting her lip as he couldn't help but fondle her expanding assets.

"Is this enough? D-do you want me to keep going?" Sarah asked, her voice shaking with a mix of excitement and uncertainty. "Just say the word, bro."

John could only watch in wonder and hold on as he felt Sarah's breasts grow, going from ripe apples, to a good handful, then overflowing into a D-cup under his hands. He kept watching and fondling until they finally reached a size that threatened to overwhelm her frame. Only then did he manged to stammer out a single word: "Stop."

Sarah's breasts immediately ceased growing, John feeling them almost jerk to a stop in his hands. He let out a shaky breath as he tried to process what had just happened, hefting Sarah's now massive breasts in his hands, marveling at their weight and softness as he explored every inch of her new, enhanced cleavage.

"Oh God, that feels amazing," Sarah moaned, her head lolling back as John's fingers toyed with her sensitive nipples and squeezed her expanded globes. "I had no idea you could use me like that."

John looked up at his sister, a wicked grin spreading across his face. "Neither did I," he said, his voice filled with mischief. "I wonder what else I can do."

Sarah shivered in anticipation, pressing her new assets harder into his questing hands, her nipples hardening even further, as if trying to poke a hole through the hands groping them. "How else would you like to use me?" she said, voice husky with desire.

AI Note:
The AI ran away with a typo I made on breast size (I had said they were B-cup in character description but typed D here) and I decided to go go with it. At this point I was just playing around and trying to learn the system since I knew I wasn't going to get this attempt to accept any of the previously written chapters.