Zoe's eyes flicked down to my ridiculously-oversized junk, lingered a little too long, and then flicked back up to my face.
"You... can explain?" she asked, slowly.
"Just let me inside the house," I pleaded, "and I'll explain everything!"
"Okay," she said, fumbling for her keys. She kept looking at my giant cock. I felt humiliated. Even worse, I was getting aroused by being humiliated. I didn't know this about myself before, but I did not want to get aroused while naked in front of my sister.
Zoe finally got her keys out and unlocked the door. I tried to rush past her and get inside the house, but I managed to crush one of my huge balls between my thighs and ended up stumbling towards the door instead. I leaned against the doorframe, blinking back tears of pain, and Zoe held the door open for me.
"Thanks," I gasped, and lifted my massive balls in front of my legs with one hand so I could walk. I used my other hand to lift my foot-long penis so I didn't accidentally bump Zoe with it as I went past, and then I raced upstairs to my room. Well, "raced" is the wrong word - I kind of frog-hopped my way up the stairs, trying not to crush my balls again. I got into my room and tried to close the door, but Zoe was right behind me. She stuck her foot in front of the door and held it open.
"Not so fast," she said, "You owe me an explanation."
"At least let me get decent first!" I pleaded, but Zoe just shook her head.
"It's not like I haven't seen everything already anyhow," she said. "You can sit down and explain this to me right now, or I can start taking photos and figure it out myself." She pulled her cell phone out of her bra and pointed the camera at me.
"No no no!" I stammered, and sat down on the bed, pulling a blanket over my cock. It still stood at attention, making a rather large tent in my lap. It stuck out nearly as far as my knees.
"Okay," I said, trying to keep calm. How much should I tell her? "First off, I was given a... a curse."
"A curse?" Zoe said, raising an eyebrow.
"Yeah," I replied, "A curse. Like, magic. I can change parts of my body into whatever I'm thinking about, but I'm not very good at controlling what I think about."
"So you were thinking about a giant cock?" Zoe asked.
"No! Well, yes," I said, sheepishly, "but not on purpose. See, I was at Karyn's, and she was making me transform..."
"So you transform into whatever people tell you?" Zoe asked, looking at me very intently.
"No," I said, "Just whatever Karyn tells me... ugh, it's hard to explain. Anyway, Karyn made me take my clothes off and was making me change, when her parents got home..."
Zoe interrupted me again. "So if I told you to think about giant boobs, you would grow a pair of giant boobs?" she asked.
"No, only if I concentrate on it. As I was saying, Karyn's parents..."
Zoe typed something into her phone as I was talking, and then turned the screen towards me. There was an animation of a topless woman massaging a huge set of fake boobs on the screen. I lost my train of thought for a moment, then felt a weight start to build on my chest. Shit!
I looked down and saw two large, firm tits growing on my chest. I grabbed them and tried to push them back in, but they just squished around my fingers - just like the lady in the animation on Zoe's phone. God that felt good. I felt my dick, which had started to soften slightly, get harder again.
"Holy shit!" said Zoe. "So I can make you transform?"
"No!" I shouted, "I'm in control of it! Sort of. It's just hard for me to stop thinking about a change after I start! That's why my dick is so big!"
Zoe looked at me, puzzled. "Why couldn't you just think of having a really tiny dick, then?" she said.
"Because I don't WANT a really tiny dick!" I shouted, but it was too late. The tent in my blanket vanished. "Fuck!" I said, trying to see past my huge boobs.
"Wow, your nipples are really nice," Zoe said.
"Huh?" I asked, and looked at the nipples on my new tits. They were nice, actually - hard, pointy, and a lot bigger than my normal nipples were. Unfortunately, Zoe's question was a ruse - while I was looking at my tits, she whipped the blanket off of my lap, leaving my cock hanging out in the open.
I couldn't see it past my tits. I grabbed one with each hand and pulled them to the sides, to evaluate the damage. It turned out that "hanging" was the wrong word for what my dick was doing. It was still rock-hard, but it barely poked past my pubic hair. Holy crap, it was tiny! It couldn't have been more than two inches long!
"It would be easier to see if you were bald down there," Zoe said with a grin, and before I could get my thoughts together, I was imagining my crotch being completely hairless. My tiny cock now stood out clearly.
"Stop it, Zoe!" I said. I tried to concentrate on my normal cock, but Zoe said "Hey, be glad I didn't try to get you to think of a tight, hairless pussy or something."
My cock, or what little was left of it, shrank to nothing as a slit appeared where my balls had been a moment before. I slammed my legs together, hiding my new pussy.
"Wow, you're an ugly girl, Jon," said Zoe.
"GET OUT!" I yelled at her, trying to get up off the bed so I could close the door.
"No, you still owe me an explanation," Zoe said.
I let go of my tits and jumped to my feet. Zoe turned her phone around and pointed the camera at me again.
"I'm recording this on video!" she shouted, gleefully.
"Stop!" I yelled, trying to grab the phone, but Zoe backed out of the room. She turned and ran towards the stairs, holding the phone over her shoulder to continue recording. My massive boobs bounced uncomfortably as I chased her, slowing me down. She ran down the stairs and I chased after her, trying to grab the phone out of her hand. She went around the corner, and I chased her. Then I stopped, as I saw Karyn standing in the wide-open back door.
"Jon!" said Karyn, "I got here as soon as I... what the hell?"
