Jeff was shocked how hard he came as he could not stop coming inside his girlfriend sperm was running down his shaft as her pussy could not take anymore. Suddenly Mary cried in pleasure as all her muscle tensed and more and more pleasure build in her. "MORE!", she screamed as Jeff noticed something odd going on. All of Mary's long tentacles were pulsating as she stretched them in all directions. Slowly Mary guided instinctively some of her appendages below Jeff and wrapped them around him. Jeff snapped back to reality when he realized what was going on. Somehow his sperm must contain the stuff from the vials and now also affecting Mary. In fear he watched her continue to pulsate when he noticed that she grew.
I've to stop this!, thought he as he tried to lift Mary off his penis but it was to late. She hold her wrapping tight around his waist and even with all his big muscle, he was not able to push her up. She was definitely stronger than him now. Mary noticed that Jeff stopped fucking her and started to feel the tight pain in her limbs. "Whats happening?", she asked herself. Then she also realized that she was growing stronger with every second. "Jeff, what have you done? I feel great. I feel so strong and powerful? Whatever caused you to grow, is now affecting me."
Jeff grabbed one of her noticeably wider tentacles and squeezed it with all his strength. He was able do push a little dent into it but then it got insane hard. "What are you doing Jeff?", she asked, "pretty hard eh?" Mary growth came to an halt and she slowly lifted herself off his still hard penis. Jeff was somehow happy, that her growth had stopped but still was a bit afraid and marveled how strong she really got. His question was soon answered as she released all but one tentacle of him and pushed herself up. It looked like she was floating above him. "Wow, I'm so strong now", she said excited, "I don't feel my own weight". Mary then moved two of her appendages on the floor pushing herself up while still holding Jeff. "Ha, this cant be true", she grinned, "You also feel almost weightless to me honey." She extended further her tentacle and pushed her 7 foot giant boyfriend several foot up, until his head hit the ceiling. Helplessly, he hold on the one tentacle in fear, that she my let him fall.
Mary examined here body. Her tentacles must have doubled their diameter, making them about two inches wide. From his pathetic try to squeeze one of them, she assumed, that her musculature reached new degrees of density and strength. Below the soft skin were rock hard inhuman muscles. She must also have gained some of her old size during her growth, but compared to the giant Jeff, she was really tiny. Tiny but strong.
"I think you've found a vial that causes all your growth, or? And when you came in me, some of the serum also got into me... But my musculature before was beyond human levels so the growth were super effective to me. Remember, I'm almost made of muscles. And I like it. You can not imagine how strong I've become. Heck, I don't even know how strong I've got", she said, still holding Jeff overhead with one of her tentacle. She lowered Jeff towards and gently gave him a kiss, "I've should be upset that you betrayed me but you caused also this wonderful growth".
"And you know the best", she said, "I'm still in my soft form..."
Jeff eyes snapped open. Her soft form? Shit!, thought Jeff and gulped. Jeff watched as Mary slowly began to change again. She lowered herself and Jeff to the ground as her tentacle retracted. With every second, they got shorter but wider. Her skin darkened as she continued to change to her human form. Her arms and legs grew in size as they got more defined. Muscles were growing again all over her body as she got more solid. She slowly stood up as her limbs were now fully formed. Her legs and arms looked toned and even unflexed very powerful. Mary slid with her hands over her body and was turned on by the feeling of her hard muscle. Her abs were well defined, she had a nice defined biceps and she looked stunning... and powerful. She pressed her fingers on her abs which felt steel hard. Overall her body grew near to her original size, but with far more defined muscles.
Mary reached out to Jeff with both her hands and effortlessly lifted him up off the ground, spinning him around like a little child. "This is insane!", she joyed. She let him go and started to lift be bed with both hands eventually released one, then the cupboard, and the whole wardrobe... nothing seemed to challenge her even a little bit. "Wow, I'm really a lot stronger than I look.", she said.