You need to drink her smoothie.

“Refresh my memory, what do I need to do, *big* sister?”

Kary smiles. “You already know, because you started already.” Her smile brightens. “But I’ll say it out loud, if it will turn you on. My cum contains large amounts of estrogen and growth hormones. You need to get them in you and on you, like when you ate that dollop of precum earlier. I suspected you wanted this after you knowingly had your first dose. So when you kept feeding me, I knew you wanted me to expose my body for you, and I played along. And here we are. Why don’t I help you get undressed?”

Kary attacks your pants to unbutton them and you pull off your shirt. You lean back still mounted on Kary’s cock and slide your legs out.

“No underwear? I might start to think you planned on this happening!”

“Kary, you didn’t have any either,” you remind her. “What did *you* plan on?”

“Why, just some quality time with my brother, of course! Then masturbation...I can’t cum at school since I make so much and the, uh, side effects if it got on anyone. I’m so full right now. I wonder if my need to unload is clouding my judgement?”