My sister and I are twins, so we were very close growing up, we didn't have many secrets with each other. Growing up our bedrooms were separated by a bathroom that we both used. Because we were so comfortable with each, neither one of us hardly ever lock the door. It was no big deal to go in and use the toilet while the other showered.
My sister Amy was the shy one. She never dated much, and I was sure she was still a virgin as we turned eighteen in our senior year. She was very pretty with long brown hair and blue eyes, and over the last couple of years, I couldn't help but notice how well she filled out her bathing suit.
I had the same hair and eye color, with about four inches of height over her. With the working out I was doing, I thought I looked pretty good in a bathing suit too. I was definitely the more outgoing on of us. I had had several girlfriends, done different things with some and managed to have sex with one of them.
I had gotten up one Saturday morning and had to pee. I heard some music playing and the water running in the shower, so still just in my boxers, I knocked and opened the door
"Hey Amy, I'm coming in."
I just finished relieving myself, when the water shut off. I turned just as she whipped open the curtain. Her head was down as she pawed around looking for the towel. My mouth dropped open as my eyes took in the sight of my naked sister. She was absolutely perfect. Her breasts had to be a c-cup with larger nipples than I'd ever seen before. Her abs were flat with just a hint of muscle showing. She had just a hint of hair above her shaved pussy.
That was when she noticed me and let out a screech and put the towel in front of her.
"Jim! What are you doing in here?"
"I'm sorry Amy. I just came in to pee. I knocked and hollered like always. I'm leaving."
I noticed she was staring at my crotch as I walked out. I looked down as I closed the door to my bedroom. I had a full-on erection causing a tent in my boxers.
"Oh great." I thought. "Now she's really going to think I'm a perv."
I sat on my bed with my cock refusing to go down, when there was a soft knock on my door. I hurriedly put a pillow over my lap before telling her to come in, still wrapped in the towel.
"Jim, this was my fault, with my music playing and water running, I didn't hear you come in."
"I guess we're both at fault, I should have waited until I knew I was coming in."
"So, this is going to be awkward, can I ask you a couple of things?"
"Sure Sis."
"I saw you had an erection when you left. Was that because of me, or a morning wood kind of thing?"
"All you Amy."
"And judging by the pillow placement, it's still there?"
I just nodded.
"This is going to sound weird, but can I see?"
"What?"
"Just move the pillow. I've never seen a guy with an erection before. I'm curious."
With all the talk about erections, my cock was throbbing. I was frozen in place. She reached for the pillow.
"I'm going to move this unless you stop me."
She slowly dragged the pillow away revealing the tent in my boxers.
"That looks so cool! You're really stretching your boxers out."
The she pouted a little.
"The only problem is, I can't really tell what it looks like. Will you take your boxers off so I can get a good look?"
"Are you crazy?" I asked.
"Well, you saw me naked, so it's only fair."
"For like a second."
She reached for where her towel was tucked in.
"Okay then, how about I drop the towel and you drop your shorts, and we can both get a good look at each other?"
I knew it wasn't a good idea, but I was eighteen and horny, and dying to get another look at her body.
"It's a deal."
I stood up and hooked my thumbs in my waistband. She untucked her towel. I shoved my shorts down and she let the towel drop. We were standing there naked, staring at each other.
"Oh wow! It looks better in person than any pictures I've seen of penises. I know you've seen naked girls before; I hope my body is good enough."
"Yours is the best one I've ever seen. You're beautiful!"
I noticed her nipples had become more erect than when she stepped out of the shower. We spent several seconds taking in each other's bodies.
"You really think so?" She blushed a little.
"I really do. Can I see your ass?"
She raised her arms above her head and turned around, giving me a nice view of her naked ass.