But his butt is just so good

Emily looked at Alex and felt her cock demand more of it's little sis. Unfortunately even new to the whole cock thing she knew she couldn't get hard after getting such a satisfying blowjob. Then she remembered the marker and after a frantic search put the tip to her skin and stopped. She remembered Alex detail the rules so she thought of exactly what she wanted. and what she wanted to to get hard whenever she want and only when she wanted, and to be able to cum as many times as she wanted. She tried to think of how to write that down.

She settled on 'PERMANENT COCK CONTROL'. She looked at the black writing and taking a page out of Alex's book, well arm, wrote 'PERMANENT INVISIBLE INK'. The words disappeared unless she thought of them and grinned. She then looked down at her cock, and saw Alex still between her legs looking up at her with his cock hanging slightly agape above her mouth. She made her cock hard and Alex let it invade him without moving. His staring up her with those big eyes as his lips locked around her cock and he began to suck without question or comment.

She watched as his head bobbed on her cock head. It felt amazing but she wanted more. She'd seen her little sister's face with a cock down his throat she wanted to see how he looked with her cock somewhere else inside him. Her hands on his head stopped his bobbing and looked up at her in an adorably unsure manner.

"Ride me little sis." Emily said and watched as Alex's face lit up. He scrambled up her body and put his legs on either side of her. His little dicklet pointing up at her as she felt her cock pushing against his butt plug. The heart shape blocking her access to his boi butt.

She reached between their legs and pulled it out. She threw it away, anger something had slowed her fucking. She pushed Alex's hips down and felt her head strain against his tight little butt. When her head popped inside her previously deposited load worked as lube. She made him bounce a few times spreading her cum along her shaft to make slide in easier. That done she lifted him up so only her crown was inside him, feeling him squeeze her cock with his butt with each of his heart beat made her want to spend the whole day inside him. Not fucking just using her little sis as her personal cock warmer.

Alex did not feel the same as the second her hands loosened he plunged down on her cock letting out a moan that made her cock pulse. He began to bounce on her lap with the happiest expression she had ever seen plastered on his face. She felt something wet on her stomach and looked down to see his soft dicklet flapping around spraying ore everywhere.

She thought it was adorable to watch and pushed his chest back a little to get a better look at such a cute little sight. Alex leaned back and she felt his hands rest against her knees. The change made him slow his bouncing and Emily thrust up to remind him of his purpose. He got the message and quickly got back into a rhythm.

She looked up at his face. He really did looked like a girl. Even his dicklet looked feminine. She reached down and pinched it between her fingers getting a massive groan from him as he felt her grasp just below his head.

"You are such a pretty girl." Emily moaned as her fingers were painted with pre.

"I'll be your girl big sis." Alex replied, taking his hands off her knees and leaning forwards, not enough to obstruct her view of his dicklet but lined up their eyes.

"You could be." Emily said as her hand found the marker. The thought of taking so much control of her little sister that she could change something this major and he would love her even more for it.

The thought was too much and she shoved her hips upwards and flooded his ass for the second time. She finished quickly and looked down hoping to catch him cumming. He was still slowly riding her and showed no signs of cumming. He was slowing down, apparently not cumming was ok so long as she filled him up.

She would have none of that, if she could get her little sis of with a butt fucking what kind of loving big sis would she be. Alex seemed to notice both her sudden determination and the fact her cock was still rock hard inside him.

She took control now standing up and taking Alex with her. She held his hips as he wrapper his hands around her neck and held on. She began to pound him using all the momentum there was to fuck faster. The sound of their hips meeting filled the room as Alex's head lulled back, her cock pushing all the right spots so rapidly he couldn't even think beyond his need to take as much cock inside his butt as possible.

He didn't last much longer and soon Emily felt the ever increasing wet patch suddenly explode. She looked down to see his dicklet milked of all the cum he had. He began weak and almost slipped off her when she grabbed him. Looking at him she pulled out and moved him onto the couch, she pointed her cock at his dicklet and came. The volume of cum she dump onto him compelely covered him. Looking up he looked even more girly, cum dripping from his butt, his dicklet hidden by cum and his mind trying to recover from the orgasm.

The marker found it's way back into her hand and she looked down at him. She could just write 'GIRL' she liked his dicklet but now she had a cock, she wanted to fuck a pussy. But she didn't want to fuck some random girl she wanted her first time to be special, and with Alex.

She decided that when her little sis recovered she would talk to him about this.