Is semen.

Gabriel was really smug about the situation. I was too afraid to get mad at him at this point, I was only hoping the side effect wasn't serious.

“So, the potion activates the change of your body, but the thing is it needs fuel to keep the transformation active.” Gabriel explained while I listen intently. “Every twelve hours or so your body will revert back to it's former self, and if that happens it will be permanent. Even if you drink more of the potion it won't take, you need the fuel from here on out!”
“Okay so what's the fuel?” I asked, still getting used to my new sexy voice.

“Semen.” I must have had a disgusted look on my face when he told me because he laughed hysterically.

With how I looked before, and my introverted personality, I've never even kissed a boy, let alone do anything else. Now I needed to drink semen every 12 hours!

“I drank the potion last night at nine, that means I only have an hour. Where am I going to get semen in one hour!”

That's when Gabriel just smiled as he unzipped his fly and took out his penis. I couldn't help but stare at him in shock. Was I really considering doing this. I barely know this guy and he wants me to... do stuff with him!

“I don't know about this...” I said as I backed away from him.

“Hey, if you don't want to do it then you can just have your old body back forever.”

That sentence made me pause. I took a deep breath, and walked back over to him. His dick was hanging low out of his pants, but it didn't look all that unsatisfying. I knelt down in front of him to get a better look at it.

“Tell me what to do.” I looked up at him with expectant eyes.

“Ooh, that's what every man wants to hear.” He laughed. “Start with your hand. Just stroke it.”

I did as he said and took his dick into my hand. It was soft and warm, but as I started to stroke it got harder. Soon it was twice the size, and I was transfixed by it. I'd never seen a boys penis, let alone feel it grow between my fingers; it was kind of exciting. I made a fist around Gabriel's shaft, and started to pump it harder and faster. Somehow it was coming naturally to me now, I just knew what to do. I saw a small bead of clear liquid emerge from the tip, and I remembered from Sex Ed that this was pre-cum.

“That's it. Use your mouth now.” Gabriel encouraged me.

I looked up at him, then back to his hard cock. Something about it was intoxicating, and I wanted to taste it. I parted my lips and took the dick into my mouth. The sensation was surprisingly pleasant, the soft skin glided past my lips and the slippery pre-cum smeared onto my tongue. Gabriel seemed to enjoy this and began to thrust his hips against me. His cock filled my mouth, and I began to salivate to accommodate it.

Instinctively I sucked my cheeks in to massage Gabriel's cock, and swirled my tongue around the tip. I felt like I wasn't even in control. I slurped and sucked on his cock like it was a lollipop, and all I could think about was the cum inside it. Gabriel grabbed my head for support as he fucked my face. My nostrils flared trying to get air into my lungs since his cock was occupying my mouth.

I felt a tingle between my legs as I sucked and licked every inch of Gabriel's cock. My hand darted to my pantyless vagina, and I felt the wetness on my lips. I was about to start masturbating when suddenly Gabriel moaned. Without any more warning than that my mouth was filled with thick hot cum. Without any shame at all I swallowed it, and I was rewarded with another gushing load, and another. I gulped all of it down, the sticky mess coating my throat and warming my belly. I don't know what came over me, the only thing that stopped me from gobbling down all that cum was Gabriel finishing and pulling his cock from my mouth.

“Ah, damn! That was good.” He slumped back against the wall.

I could only sit there on the floor, reveling in the moment. The pungent aroma of cum emanated from my lips, and the taste in my mouth was oddly delicious. I licked my lips, trying to get more of the flavor onto my taste buds.

“Haha, yeah it does that.” Gabriel seemed to notice my attempts. “It alters your taste of semen. Some of the girls tell me they even crave it like a ****.”

“Girls?” I asked him.

“Yeah. What you think you're the only geeky school girl who wants to be different?” Gabriel then told me about three other girls from our High School that took the potion, girls that I envied! If only I knew then what they were doing to have those looks and popularity.

“So, I won't change back now right. At least not for another 12 hours?”

“Yup. You need about one guy's load every 12 hours. And if you have more than that it should extend the time. Katie told me she drank 8 loads before she went on a weekend trip with her family, and she was fine once she got back.”

“Alright... Well, thank you. This is actually the best thing that's ever happened to me. I love it!”

“I'm glad. Enjoy it.” Gabriel zipped up his fly and headed to the door. “If you're ever in a tight spot and need a load, let me know. Oh and before I forget, you don't need to drink it. You just have to get it into your body, vaginally and anally works too.”

Just then the bell rang so I got up and adjusted my skirt then headed for class. Hopefully no one would notice the stench of cum in my breath.