His Sister does for him

He was about to reach down and jerk off when he heard the door knob to his room turn, he turned to say something, remembered his current state, and went to cover himself then the door opened and standing there was Myra who was now quite busty. "Mark look at this my-!" she began then she saw him one hand on his blanket to pull over his huge dick. Mark realized on retrospect this would've been pointless with how big his dick was. The moment was frozen for about 20 seconds then Myra stood up straight walked in, closed the door and walked to her brother. "So something is going on here." she said, "I don't know what and right now I couldn't care all I know is that now," she grabbed her top and pulled it off letting her new E-cup sized boobs bounce free. She held them up, "Nice huh? Honestly I'd want them even bigger but I'm cool with this too!" she said, "Not to mention..." she turned dramatically and pointed her thumbs at her butt. "THIS!" her butt was no longer flat it was big and plump... 35 inches probably. Mark knew for sure now his power had worked on his sister too... which meant he could make her bigger... but not now.

The last thing he needed now was his sister figuring out his power and abusing him for her own goals. "N-Not bad sis." he said.

She looked at him then she smirked, "Right I forget you're into really big boobs... well they may not be your size... but you have to admit." she grabbed her tits and hefted them up they were much fuller than the typical E-cup bust and that made them bigger and rounder, almost like implants. "They are pretty neat." she thrust her chest into his face. Mark swallowed, and nodded, Myra backed off slightly then knelt down to look at his groin, "Now this is neat... this wasn't this big before..." she breathed in the musk it was emitting and was getting wet. Despite Myra's teasing of Mark she herself was a size-fetishist herself though it wasn't quite as severe as mark it was enough that she was getting super wet from his dick, it was more or less the perfect size...not to mention his balls. She raised up both hands and cupped one of his monstrous nuts. It was bigger than what she would've preferred but hell she wasn't gonna complain just yet.

She raised her hands to his dick and began to stroke it, "Mmmm this is a nice big dick!" She cooed, she began to pump his length. Mark began to breathe heavily being a virgin he'd never felt another hand on his dick... save his own... and having his sister jerk him off was... intensely arousing. Myra was doing her absolute best to not just sick her little brother's dick._ _His dick was starting to get hard now, and as it did she moved her head back. Because he hadn't set a limit to how big his dick was hard his dick was becoming double it's soft length which was 14 inches putting it at a whopping 28 inches in length and 4 inches of girth. "Holy fuck your dick is huge!" she said.

She looked at it, it was also bigger than what she would've preferred but she had come this far. "I might as well give you a BJ at the least." And she opened her mouth wide around the huge head and engulfed it. The instant her tongue touched his dick head Mark felt a surge of sensations to his brain. His dick swelled up and his body stiffened Myra had no time to move as his hands grabbed the back of her head and **** her down his dick pumping seed directly into her stomach! She could hear the cum pumping out of his dick and into her belly from her head being shoved so far onto his dick. She felt her stomach start to expand as he pumped gallons of seed into her. She didn't know how long he pumped his seed into her, all she knew was that her consciousness began to fade from the smell and inability to breathe.

When Mark finally stopped cumming she fell back **** her belly bulging and her mouth covered in drool. Mark looked at his dick and found it was slowly shrinking back to softness. "Shit." he realized when he saw her belly. "Fuck Um... I can't let mom see this!" he said, he shrank his dick and balls, grabbed his sister and carried her to her room thankfully his parents were still downstairs, he covered her up in her blankets and went back to his room. With that done he relaxed onto his bed. With his new powers more or less confirmed all that was left was to use it... recklessly or wisely... it was up to him.