With some 'encouragement'

"You look nervous. I'm guessing you backing out of this. If so, I'm glad that you are." You say, knowing this will give her the push she needs. Having her back down would kill the mood. Upon hearing you, she glares at you and crawls on top of you.

"Oh no John! You don't get off that easy! I'm riding that cock, and nothing is gonna stop me! So you just lay down and take it! Got it?" She barks at you. This got her into it.

"Oh no! Please have mercy!" You say in a miserable tone, but inside you're just too happy for what's to come next. Sarah lines up your penis with her anus and starts to descend. As she makes contact with your member and her anus, she shakes and gasps. She then slowly slides down your cock, gasping and moaning along the way. The feeling of her ass is incredible. As she fully hilts you into herself, she moans, trying to relax and get used to the sensation of your dick in her ass. She looks back at you, forcing her grin from before.

"How *pant* do you *pant* like that? It *pant* don't matter, because I- Ooooh-I'll keep like this for a while until I'm tired." She tries to sound scary, but with you in her ass, Sarah is having a hard time thinking right now. It also seems that you don't need to 'encourage' her for anal, as that's clearly what she wants too.

Without missing a beat, she begins to bounce on your cock, moaning with every descent. The sensation is otherworldly for you as she keeps bouncing on you. You bite your lip to suppress yourself, worried that if you show any sign of enjoyment here, she'll stop. Luckily, she starts to get lost to her senses as she starts moving faster. Your getting enveloped in her ass over and over again is beginning to take you to your limits as you get closer to an orgasm.

"Oh shit! *pant* Sarah, wait! I'm getting close!" You warn her, but this only makes her go faster, she leans closer to your face, pinning your hands as she does. You then cum in her ass, the action causing you to softly moan and her to moan louder. Sarah then moves her ass away from your penis. Looking at it, you see lots of your load drip out of her ass. Damn, her ass had an effect on you. You look back to her face, her grin this time is accompanied by half-lidded eyes, filled with desire.

"Nice load nerd. Let's see how many more you can make." She says that and nothing more, other than her moaning, as she reinserts you back into her ass and rides you the whole night. Eventually, you start to get tired and black out.