The offer

Back to Luna, he went, and Harry kept by the rules, no matter how frustrating it was. Just the sight of the three naked sweaty women was enough to keep him hard, and the constant changing sensation was driving him mad. Slowly the fear of knocking up one of them left his mind as he fucked Luna, Hermione, and Ginny, then Luna again in succession.
After seven rounds Harry was panting hard and found his orgasm was almost constantly almost there. The three witches just smiled at him, Luna with her weird bliss, Hermione with pure content, and Ginny with a kind of need in it that almost scared him off, were it not for the fact she was the most eager of the three to respond to him time and time again.

At the tenth round, Harry could take no more… he slid out of Ginny and nearly bottomed out in Luna in a single thrust, and rapidly pumped her cunt. His orgasm was so close, then just as it started to come… “Bing!”
Over to Hermione he went and tried to bring himself to orgasm again. “Please… fuck me back,” he whispered to her. Hermione just smiled, and Harry moved as hard as he could but there went the timer… “Bing!”