Give her a good grope

In order to make fingering her own ass a bit harder for his sister Adam decides to reach down between her arms and begin tugging on her now growing, previously tiny tits. At first she moans appreciatively, enjoying the attention her sensitive nipples are getting, then he yanks firmly downwards which elicits a sharp yelp from her. Never the less in her horny state she simply continues to do as her brother told her too and continues to open up her virgin ass with her own fingers by slipping in the second one, her middle one.

As soon as the second finger disappears up her tight ass, Adam tightly pinches both of her nipples (one in each hand) and twists both of them at the same time. Her face turns bright red immediately and she lets out a shriek of pain and stops fingering herself.

"Something wrong slut? Because if you don't keep fucking your ass for me then you'll never see another orgasm again"

"No, No I'll be good"

She begs looking increasingly pathetic as she bowed to his every want and need. Adam smiled as she forcefully rammed her thrid finger into the tight hole. This was going better than he hoped for, he couldn't wait until his sister had tits on her so big she could barely move.