When Ty got home from school, he did his chores, then started on his homework. As he was doing that, he heard a knock at his door. The portal door, which led to Lisa's bedroom, in her house several blocks away. "Come in," he said. Lisa opened the door and stepped into his room. "I'll be done with my homework in a few minutes, if you don't mind waiting."
"No, I'm hot and bothered right now!" she replied. He looked at her in surprise. She was smiling, and chuckled. "Just kidding," she said. "Go ahead and finish." She went back into her room, but left the door open.
When Ty finished his homework, he entered her bedroom. "All done," he said. "Now what's this about even more extreme transformations?"
"Well," Lisa said, "When I was tiny, and inside your cock, and you ejaculated me out, that was good. And when I _was_ your cock, that was even better. So I got to thinking about how to go even further down that path."
"Further? How could that be possible?" Ty asked.
"What if I was your cum, and you ejaculated me out?"
Ty was very taken aback by the idea. "Well, yeah, I guess we could do that," he conceded. "What if not all of you came out? What if some of you soaked into the bed sheets or something?"
"I suppose you'll just have to make sure you ejaculate me all out, and make me not soak into anything."
"OK," Ty said. "I guess I can do that. This really does sound quite extreme. Are you sure you want to do it?"
"Yes!"
"Alright, here goes," he said. Lisa's body started shrinking, and he felt a tingling in his balls. Before long, her human body had shrunk away to nothing. He walked back into his bedroom, undressed, lay down on his bed, and started masturbating.
Before he got very far, there wss a knock at his bedroom door. The normal door. "Ty, could you please bring in the groceries?" June asked.
Ty grumbled under his breath, but said, "Sure, Mom! I'll be down in a minute." He quickly got dressed and went downstairs. June was in the kitchen.
"Are you and Lisa busy tonight?" June asked. "We might play board games after dinner. And of course she can have dinner with us, if she likes."
"Um, I'll ask her when I see her," Ty replied. Although Lisa was inside his balls at the moment, he didn't think she had the ability to hear the conversation. He started carrying in the groceries from June's car, and putting them away.
When he was done dealing with the groceries, he went back to his room, undressed, and started masturbating again. At first he wasn't too excited about it, but as he thought about Lisa being just his semen, he started getting more into it. Before long he started to come. He shot out more and more ropes of cum. He was astounded at how many times, how much cum there was. It didn't seem like it was ever going to stop, and the pleasure was intense. Finally his muscle contractions started lessening in intensity, then ceased.
He saw one large pool of cum on his bed, and several smaller ones. There was some cum on his body. As he watched, all of the cum that wasn't already in the large pool started running toward and into it, until all of it was together. It started changing into a more solid form. Before long, it looked like the featureless blob form Lisa had had partway into mattress topper form, though smaller. She continued to transform, until she had her human form back, but at a smaller scale, about four inches tall.
"Was it as good as you expected?" Ty asked.
"Oh, even better," she said, smiling.