When I was nineteen, my family went to a costume party. I had always thought those were lame, and I wasn't looking forward to wearing a costume. So I was going to hide somewhere and wait the party out. But when we got to our friends' house, there were already a ton of people there. It looked like the whole neighborhood showed up.



I groaned inwardly and went inside with my parents and my older sister. She was two years older than me, and was kind of a health nut. She was always watching what she ate, and she probably had the best body I had ever seen because of it. She wore this big tiger suit to the party, which was way too big for her. She could barely get around, and the mask was huge, she looked like a giant stuffed doll.



I was wearing some stupid alien outfit that I had found in our attic. It was way too small for me, and within the first few minutes I ripped it. I wasn't exactly enjoying this party.



My sister, Erin, found me sitting quietly in a corner. She had a drink in her hand, which she could barely hold through her tiger costume.



"Hey," she said. "What are you doing all the way over here?"



I shrugged. "Just waiting the party out."



She handed me her drink. I took a sip, and winced. It had a lot of alcohol in it. She always let me try her drinks, even though our parents didn't like me drinking underage.



"There isn't anyone here for you to talk to? No cute girls?"



I rolled my eyes. "Gimme a break. I don't see you with any guys."



She sighed. "Yeah, you're right. This neighborhood sucks."



I took another sip. "I ripped my suit too."



She looked at the tear running up my leg. "I think you've outgrown the alien suit."



"You look like you're drowning in that thing," I said to her.



She pulled her mask off. "Yeah, it's hot in here too."



She took a drink, and we were both quiet for a while. Then Erin smiled.



"You want to have some fun? Get in here with me."



I was a little surprised. She wasn't usually this "cozy" with me, maybe the alcohol was affecting her. But I was never one to turn down intimate contact with a hot girl.



"Are you serious?" I asked.



She shrugged. "Yeah, it'll be fun. There's definitely enough room in here. We'll see how long it takes for Mom and Dad to find you."



She tried to reach her back to unzip the costume, but she couldn't stretch that far.



"You'll have to unzip me, I couldn't get it on by myself either."



I pulled the zipper down, and saw that she was wearing only a bra and panties underneath the costume. I was a little nervous. Erin waited for me to finish unzipping, and then she must have remembered what she was wearing.



"Oh, sorry, I forgot I'm in my underwear. It gets so hot in here, and I figured I wouldn't be taking it off anyway."



I didn't know if she still wanted me to climb in or not, so I didn't do anything.



"Well," she said finally. "Go ahead and get in, I won't back out now."



I pulled the zipper all the way down to where it ended just above her ass, and stepped into the costume behind her.



"Wait," she said. "Take your alien suit off, there's no way you'll get in here with that."



I hesitated. "But I'm not wearing much under here either."



She shrugged. "So what?"



I took another look at her panties, and the shapely ass inside of them, and immediately took the suit off, glancing around to make sure no one could see us. I threw the alien suit into the corner and stood there in my boxers. I stepped inside the suit and suddenly felt the warmth from Erin's body. I was pressed against her backside, and my crotch was lined up right at her ass. It was a little embarrassing, but I quickly reached behind me and zipped the suit up.



The mask was a little bit of a tight fit, and my face ended up in her hair, but I was too distracted by the feel of her body pressed against mine to really care. She adjusted to the feel of both of us inside the suit.



"This is so funny," she said. "Can we even walk in this thing?"



"Try it," I said. "Just start walking and I'll follow your lead."



She stepped forward, pulling my leg with hers. We got the rhythm down and started walking. It must have looked funny on the outside, but no one was paying attention to us. Having her warm skin touching me all over was exciting. The feel of her body crushed against mine was starting to turn me on. Suddenly Erin stopped walking, and just stood there.



I wondered why she had stopped, and then began to realize I had an erection. It was lodged firmly between her ass cheeks, with only my boxers and her panties between us. She just stood there, and didn't say anything. I felt her ass move a bit, probably to see if it really was my dick pressed against her. But she didn't say a word.



Then, a few moments after she had stopped, she started walking again. She still didn't say anything, until we reached the stairs.



"I have to go to the bathroom," Erin said.



We struggled a bit going up the stairs, but we made it to the bathroom. I unzipped the costume and shut the door behind us.



We both breathed in relief a bit, after being closed up inside the hot tiger suit. Before I could say anything, Erin stepped out of the suit completely and went for the toilet.



"Do you...want me to leave?" I asked.



"Are you going to stand in the hallway in that suit? It'll give us away."



She lifted the lid and pulled her panties down, right in front of me. I couldn't help but stare at her, she didn't even try to cover herself up. She sat on the toilet, her eyes wandering to my crotch. I followed her gaze, to see my erection quite obviously pressing through my boxers. The suit had sagged below my waistline. I pulled the suit up, hiding myself from view.



Erin finished and washed her hands, and then came back over to me. She just stood there, not climbing back in just yet.



"Geez, it's pretty hot in there, huh?" she said.



"Yeah," I said.



She just stood there, looking down at where my crotch was. I had the suit covering me, but it was obvious she was looking where my erection was.



"Do you need to...you know?" she asked.



I didn't know what she meant.



"What?" I asked.



She looked up at me with a bit of a smile.



"You know," she said. "You look like you need to...relieve youself."



I couldn't believe what she said. "What? No, I don't...I mean, of course not. I'm not...it's not you..."



"Well of course it's me," she said. "I just didn't know if you were...hard, you know, because you needed to."



I had never been more embarrassed in my life. "I'm so sorry, I didn't mean to...you know."



She shook her head. "No, it's okay. You know what?"



Just then she reached behind her back and unhooked her bra. She took it off right in front of me, and threw it aside. Then she hooked her thumbs inside her panties and pulled them down. I watched in total shock as she kicked them off and stood before me completely naked. I had always thought she had a great body before, but to see her naked like this was so much hotter!



She paused for a second, as if to give me a full view.



"Don't say anything, just take your shorts off," she said.



I was too shocked to argue, and I instantly complied. Erin's eyes were glued to my dick. She couldn't take her eyes off of it. I felt kind of shy, but proud at the same time. Then she climbed in the suit and once again our bodies were pressed together as we zipped up. Of course, it felt completely different being naked, my dick burying itself between Erin's ass cheeks. She felt much warmer too, and as we adjusted to each other again, I know I felt her move herself against me more sensually. Maybe she was getting off on this. What was I saying, of course she was. Why else would she have taken off her underwear?



I instinctively thrust my hips forward, and she pressed back against me.



"Are you sure...you don't need to?" she breathed, her voice huskier.



I kept myself pressed against her. "I don't think it would help me any."



We stood there quietly, in front of the bathroom sink, crushed against each other. We were both breathing heavier, and Erin was clenching her ass around my dick. I felt brave and made the first move. I thrust my dick further up her ass crack, and then slid back down. Erin gasped, obviously enjoying the sensation. I did it again, and she again responded with increased arousal.



I began sliding up and down between her ass cheeks, fucking her ass without any penetration. She braced herself against the countertop, leaning forward while I thrust into her ass. It felt great, and I was already so hot from seeing her naked that I felt my loins stir.



"Wait," I said, "or I'll cum."



Erin didn't say anything, she completely ignored me and kept thrusting her ass back at me. I took that as a sign to continue and thrust into her a few more times until I boiled over.



I grunted and ground my dick into her ass, nestling it firmly between her cheeks while I shot my load. I exploded up her ass and shot all over her back. I spasmed seven or eight times, cumming more than I ever had in my life. When I came back to my senses, I felt Erin tense up, and she began to shudder and groan. It took me a few seconds to realize she was climaxing, without even touching herself.



I waited for her to finish, and when she calmed down, I unzipped the constume as it was getting rather hot in there. Erin was panting, and I saw my cum all over her backside.



"Your cum," Erin panted. "It got me so hot!"



She turned around, still inside the costume, and pressed her crotch against mine. My dick jabbed at her stomach. She moaned pleasantly as she ground into me.



"That was so good!" I said.



"I was kinda hoping to get laid tonight," she smiled. "What do you say?"



I couldn't believe she just asked me to fuck her! After what had just happened, it seemed only logical. She grabbed my dick and guided it to her pussy. I felt her hot hole as it touched the head of my dick.



"Are you sure?" I asked.



She smiled at me and nodded. I pushed forward, slowly entering her. Her head tilted back as I slid into her. She was so hot and wet, before I knew it I was all the way in. It felt so good, having her pussy tighten around my dick. I started fucking her, and she eagerly fucked back at me.



She leaned back against the countertop, and I started pounding into her. We were really getting into it, and she started making noises that drove me wild. If anyone had been standing outside the bathroom, they would have heard her. She held onto my arms, pulling her legs out of the costume and wrapping them around me. We both watched in fascination as my dick slid in and out of her pussy. She started making a whining sound, and then she cried out as she climaxed.



Feeling her pussy clench around my dick excited me, and I felt my orgasm nearing. I glanced up at her, and she nodded as if she read my mind. Then she watched in eager anticipation, waiting for me to cum. I thrust as deep as I could and didn't hold back as I came. I groaned and released my semen into her belly. She held me tightly against her, milking me with her pussy to intensify my pleasure. I fell forward, holding her body beneath me. Her legs were locked tightly around my waist. I felt her breasts crushed against my chest, and her hands roamed up and down my back. She whispered into my ear, encouraging me as I came. I gave her all I had, and we both stayed locked together, completely spent.



Finally, I stood up and withdrew my dick from my sister. We were both sweating, but it was a good kind of sweat. Erin traced her finger lightly up and down my chest, and smiled.



"You're a good fuck," she said.



I leaned forward and kissed her for the first time. She seemed to enjoy kissing me, and I enjoyed feeling her breasts while we kissed. She leaned back and let me stare at them.



"I can't wait to suck your dick," she said.



"Let's get out of here," I said.



"I'll tell Mom and Dad we'll walk home. Let's see what it's like to walk all the way home in this thing."



"Who knows, we might have to stop and rest."



We both smiled. There was no doubt about it, we were going to fuck each other's brains out tonight.