When I was 15 years old I was left one Friday night to watch my 10 yr old cousin while our parents went into the city for dinner and a play. Since they were expected to be out until about 2:00 am, I was in charge of Mary for the night; fixing her dinner, keeping her entertained, and getting her to bed by 10:00. I was fine with it since I didn't have any plans, and she was pretty cool and we got along well since we saw each other at least a couple times a month.
Our parents left about 4:00 in the afternoon and since it was a nice day (it was summertime) we hung out in the backyard, listening to the stereo, playing Frisbee, and she was riding my old bike. After a while she said that she was hot and wanted to run under the sprinkler (that is what she would sometimes when she came over with her parents). I asked her if she brought her swimsuit with her and she said no. I told her she couldn't run under the sprinkler without it, but if she wanted to she could in her just her underwear, thinking that she would say no way and forget about it. She surprised me when she said, 'OK!' Since our yard was pretty secluded I figured it would be alright, and she asked me if she was going to do it, would I do it with her.
Now my mind started racing. Being 15 and perpetually #####, the thought of running around in my backyard in my underwear was arousing enough. Doing it with my cousin, in HER underwear, had me semi-hard in about 5 seconds. I had never given any thought to her in 'that way' before, but as I thought about it I realized that she WAS a really cute kid, and in a couple years would probably be really hot. She was pretty petite, with short brown hair, green eyes and a great smile with lots of dimples. I had casually noticed her firm, round ass the last time she had been over in the tight pair of shorts she had been wearing. As I was thinking all this I was becoming more and more aroused, even though I had already masturbated twice that day!
I quickly told her to wait, that I was going to get some towels, and I sprinted inside and quickly came back out. When I returned she was giggling and asked me if I thought it was really OK to run around in our underwear. I told her sure, no one would see us and I took off my shirt. She took the cue and pulled off her t-shirt; she had no breasts to speak of and was wearing what I guess would be considered a training bra/vest. Without hesitating she unsnapped the buttons on her jeans and stepped out of them. I momentarily stared at her in her underwear - her panties were plain white, more of a brief than bikinis, with a lace waistband that ended just below her belly button. I noticed that they were quite snug. Not wanting her to notice that I was staring at her 'that way' I slipped down my shorts (I was wearing white Hanes briefs) and we were both laughing nervously, feeling uncomfortable.
I went around the corner of the house and turned on the spigot and the sprinkler started swoosh-swoosh-swooshing. As I returned to the backyard Mary was already wet, and shrieking about how cold the water was. The very first thing I noticed was that her underwear (bra and panties) was nearly transparent from the water! I was completely hard at this point, which was obvious WITHOUT my underwear getting wet. I wondered what she would say once I went under the sprinkler since there was no way she wouldn't notice. Throwing any cares and caution to the wind, I ran under the sprinkler a few times and was immediately soaked. As I stepped out from the water and shook the water out of my hair, I noticed Mary blatantly staring at my erection.
I asked her what was wrong, and she said nothing and began running around again. I decided to keep it low key and grabbed a couple of water guns from the garage and we spent the better part of the next half hour running around, shooting each other and basically being silly. The entire time I was discreetly fixated on her see-thru underwear, noticing of course the slit of her vagina and the surprisingly large nipples showing through her bra. I caught her several times as well looking at my ####, which remained fully erect and straining at my underwear the entire time.
Eventually it got too cold to continue (the water was FREEZING), and we both decided to go inside. I threw her a towel and we went into the living room. We had both been careless and left our clothes too close to the sprinkler, so not only was our underwear soaked, our other things were as well. I told her to follow me to the laundry room so we could put our stuff in the dryer (I had an idea brewing in my head...). When we got there I told her not to look since I was taking off my underwear, which I tried to do with my towel around me. I 'accidentally' dropped the towel as my underwear was around my ankles and my ####### sprang forth. Even though I had told her not to look, the room was very small and it was impossible for her not to notice. She took a quick glance and then turned away from me saying 'OH MY GOD!' I quickly and profusely apologized, and she turned back to me as I was putting the towel around me and just giggled. Then I told her I need her things for the dryer, and I held the towel up in front of her so she would have some privacy. She kept saying 'DON'T PEEK!' and quickly shed her bra and underwear. Of course I did peek and got a tremendous view of her bare ass before I wrapped the towel around her.
I went up to my room to change (only put on boxers and a t-shirt) and she went to the guest room and put on her pajamas (all she had that was dry). I was very tempted to close the door and ######## since I was so incredibly #####, but decided to wait to see what might happen next. I was down in the living room, flipped on the TV and settled down on the floor with my back against the couch while Mary was up in the bathroom. My ####### had gone away for the time being. When she came down she immediately sat on my lap (which she had always done since she was little, but I had never been ##### for her before...). And, like every other time, she asked what we could watch on TV. I tried to focus as much on flipping through the channels to find something to watch as I could, but the feeling of her pressed up against my #### was too much. Her PJs consisted of no more that a large red tshirt then only came down barely to the middle of her thighs (which, I noticed, were very tan and shapely...) and a pair of pink panties that were very visible to me when she came down the stairs.
As she plopped herself in my lap her t-shirt of course rode up, and her sweet, firm butt covered only by her underpants (this pair was bikini...) was firmly up against my now hard-again #### - which was encased only in a pair of boxers. The feeling was heaven for a boy who had never seen a real girl naked at that point in his life (or for that matter one in underwear, until a few moments before), never even received even a ######## or who had ever been French-kissed. There was no way she couldn't feel it, but until she said something I wasn't going to move, or ask her to move. In fact, she began to very slowly but subtlety (and I think probably unconsciously) move her hips and grind back against me. This intensified the pleasure I felt and I was honestly afraid I was going to come all over her underwear. This lasted only a short time when she looked back over her shoulder and asked, 'Timmy, why is your thing all puffed up like that? Doesn't it hurt?'
Of course a million things went through my mind in a split-second, but my actual response was, 'Nah, it doesn't hurt. It actually feels really good. It's what they call 'getting #####'. It happens to guys all the time and sometimes girls. You know, that's what sex is. But if you keep doing that, you know, rubbing back against me, I'm going to have an accident in my underwear'
I'd crossed the line, and thought I went to far. She wanted to know what I meant. I told her that sperm comes out of a boys penis if he gets really excited sometimes, and she told me that her friend had told her about that just a week before because she had seen it happen to her brother. She also said she knew about sex because her mom had told her about it when she was 9.
'Can you actually make the sperm come out, Tim?'
My god, I couldn't believe it. I knew at that point I was actually going to be able to ######## in front of her. And I had an idea. I told her that I could, but it would be kinda messy and sometimes when I felt like doing it I did it in the shower cause then it would just go down the drain. I told her I could show her and told her to follow me to the bathroom. As soon as we entered, I turned on the shower. Then I told her that she needed to get in with me so she could see. At first she hesitated, but then I said hey, if you want to see me do this, and I'm taking off my clothes, you have to take off yours too.
So I quickly took off my t-shirt and dropped my boxers and she started giggling and staring at my ####. As I stepped into the shower, she stripped in no time and followed me. I made sure that she stood in front of me as she entered, and I made a point to reach forward to adjust the nozzles, causing my #### to press right up against her bare ass! I almost came right there!
After I adjusted the water temp, I took the soap and lathered up my ####. Mary was intently staring at my #######, and I asked her if she had ever seen one before. She told me she did; in a magazine they found in her friend's sisters room the previous summer, but never in person. As she was telling me this I was drinking in HER naked body; her ass was scrumptious, and I was mesmerized by her ##### (no hair, only a deep soft-looking cleft). Her breasts did show the very beginning signs of development, and her nipples were (as I could tell through her wet bra before) pronounced and large (brownish, I remember). I began to jack in earnest, and asked her if she wanted to touch it. She said no I don't think so, but after a couple of more requests and words of encouragement she reached out and took hold of it. At first she pulled back, then I gently put her hand back on and helped her with a stroking motion. When I let go, my hand lingered down her back and began to feel her ass. That was all it took - I let go with an absolute TORRENT of come. As I did so, I made sure to face her and told her to look. As my ###### began, I picked up the stroke and told her to cup her hand below my #### (the first time I called it that in front of her...). The first few spasms splashed #### all over her stomach and thighs, however the next few were perfect shots and formed a small pool of come in her hand. After 20 more seconds or so of total ecstasy, I saw that she had the handful of come and was closely examining it. I asked her what she thought. Her response: 'NEAT!' That was SO cool. You looked really funny.' And she laughed and laughed. We showered up and got dressed, and before she went to bed we had a LONG talk about how she could never tell anyone about our special shower together.
Several years later, when she was 13 and I was 18, we had one more encounter while our families were vacationing together down the shore. Another story I'll share at another time