We laid there for a few minutes, basking in a well-earned post-coital glow. After a while, my sister rolled off me, resting on her side, facing me.
"I think we better set some ground rules," she said. "Just so we both know what to expect."
"Okay," I said, not really knowing what was coming next. I was still a little overwhelmed, and more than a little spent.
"I told you I love you, and I'm going to keep fucking you for as long as I possibly can," she said. "But I'm still going to marry Todd, and I'm still going to have sex with him. At some point I'll have his children.
"You'll stay married to Lana," she continued. "She'll have your child soon, and hopefully a couple more. You'll keep having sex with her.
"Whenever it's possible, I'm going to have your cock inside me," she said, reaching down to grab the member in question. It was limp from overuse, but I still felt a stir when she grabbed it.
"What we're not going to do," she said, " is act like secret lovers. No whispers, glances, ass grabs, or anything like that. Whenever we're around anybody else, we're just brother and sister." She paused, waiting for a reaction.
"Sure," I said. "No problem." She didn't seem convinced.
"I'm serious, David," she said, her hand leaving my groin. She raised herself up on her elbow to stare at me.
"I don't want to get caught," she said. "I have no interest in marrying you, or announcing our forbidden love. I am not prepared to have our relationship become public in any way. You have to understand that."
"I do, Lisa," I said. "I have no problem with it, really. I'm still just getting used to the idea of the relationship in the first place."
"Okay," she said. "Now, let me tell you about the good stuff." Her hand went back to my now semi-erect cock.
"You can have me in any way," she said. "I'll do whatever you ask or tell me to, as long as you are nice about it. I want to be submissive, but I don't want to be called slut, or whore, and I'm not going to call you Master. Or daddy.
"You can fuck me however you want. You can cum in me, on me, whatever you want," she said. I was definitely responding to her words, and my shaft was now fully erect, throbbing painfully.
"Of course, you can't cum in me yet," she said. "After the first time I let you, you can whenever you want. Same thing with my ass. You can't fuck it until I say, but after that you can shove this inside my tight little asshole whenever you desire." I moaned.
"So when do I get to do these things?" I asked. I had moved my arm under her and was running my finger along the crack of her shapely ass.
"Don't worry," she said. "It'll be soon enough." She gasped as I ran my finger over her anus.
"You sound like you have a plan," I said.
"I do," she replied. "Would you like to hear it?" I pushed the tip of my finger into her ass.
"I would," I said. Her hand was increasing its pace on my cock, but I knew it would be a while until I came again.
"Tough shit," she said, laughing. "It's going to be a surprise. You'll love it though, I promise." She closed her eyes as I pushed my finger further into her tight ass.
"Can you give me a hint," I asked.
"Sure," she said. "Here's a hint.
"I've been fantasizing about all of this for years. I've dreamed of fucking you in so many different ways. I've watched a lot of porn, and I have about a thousand specific fantasies I want to fulfill with you.
"I'm sure that we'll get to each and every one, but there are two that are very specific. The first time you cum inside me and the first time you fuck my ass. Those two will be done according to my very detailed fantasy scenario."
"Wow," I said. "That's pretty wild."
"You have no idea," she said. I was thrusting my finger in and out of her ass now, and my thumb had found her clit. She whimpered.
"I'm going to be a totally depraved sex goddess with you," she said. "I'm going to do things that I wouldn't do with anybody else."
"That sounds good to me," I said. While I hadn't managed to be nearly as vocal about it, I certainly felt the same way.
"If I said anything like this to Todd, he'd probably leave me," she said. "He's a good lover, but he's kind of a prude."
"Really?" I said.
"Yeah," she whispered. "Sex is good, but it's pretty predictable. Usually he goes down on me until I cum, then he brushes his teeth, then he'll fuck me. Except for rare occasions when he's drunk, it's always either missionary or I'm on top.
"One time, I laid on my belly and spread my ass for him. I wanted him to fuck me that way. Not in my ass, just my pussy. He said it looked 'gross' and then just left me there." I laughed.
"That makes him an idiot," I said. Lisa smiled at me, and then kissed me. As we kissed, we both increased our rhythm on each other. Though she was new to me, I could tell she was about to cum. I wasn't that close, but I was getting closer. Suddenly, she let go of me and pulled away.
"Let's see what you'd do," she said. She rolled onto her stomach, reached back and pulled her perfectly shaped ass cheeks apart. I stared in awe at her swollen pussy lips and tight anus. Though I had never done it before, I felt powerless to stop, and I leaned in and licked her puckered asshole. She shrieked.
"Jesus," she yelped. "That felt amazing. Do it again."
I did, and she started moaning. I ran my tongue from her ass to her pussy, teasing her clit, then running back to her ass. She was squirming, pushing her ass back at me every time my tongue grazed her tight hole.
"God David," she rasped. "I'm so fucking glad you're dirty. I was worried you wouldn't be."
"Don't worry," I said between licks. "I'm just as dirty as you, I think."
"Good," she said. "Then hurry up and put your big dick in my cunt."
I was happy to oblige. I rolled on top of her, and as she held herself wide, I slid into her slippery pussy with no problem. She let out a low guttural moan.
"Fuuuck," she said as I pushed in to the hilt. "Goddamn that's good. Just stay there for a second." I was holding myself up, my pelvis pressed firmly against her ass. She pulled her hands up from her ass and stretched them over her head.
"This feels so amazing," she said.
"It does," I said. It was the best feeling I had ever experienced. I felt like I could stay there forever. She had different ideas.
"Fuck me," she said. "Deep and slow."
I slowly pulled all the way out, until just my head was inside her, and then pushed slowly back in.
