Tanya loved her tits. They were large, firm, round, and bouncy. Tanya was proud of her big, natural melons, flaunting them and showing them off in skimpy tops that displayed her inviting cleavage. Everywhere she went, men stared at her funbags, making Tanya's pussy wet and gooey.

Tanya was not the only admirer of her melons. Her melons, in fact, had many admirers. One of these was her older brother, Russ. Russ jerked off to the thought of his sisters bouncing jugs with great frequency. Sometimes, he did this with her bras, ejaculating into the cups and getting a perverse thrill from knowing that his caked semen would be touching her nipples. Other times, he jerked off to his sister's Facebook photos. The majority of Russ's sexual fantasies revolved around his sister's gorgeous tits.

Tanya was, also, a fairly stereotypical dumb blonde. Thus, when Russ confronted her in the living room, while she drank in some mindless reality series about catty women with too much money and not enough cock in the mouth to keep them quiet, Tanya was all ears.

"What happened to your boobs?" Russ asked, sounding shocked and appalled.

Tanya looked down at her expansive cleavage in confusion and asked, "What?"

"Your boobs," Russ said again, pointing. "When did they get so small?"

Perplexed, Tanya looked again and said, "They didn't. What are you talking about? Why are you looking at my boobs, anyway?"

"Don't take this the wrong way," Russ said, "but they used to be impossible not to notice. I mean, sorry, but I'm a dude. It's kind of natural to look at boobs, no matter who they're attached to."

"You're crazy. There's nothing wrong with my boobs," Tanya argued, but she didn't sound so certain.

Russ shrugged and said, "If you say so. Take it from someone who notices these things, though. They're absolutely smaller than they were."

He left the room. Tanya tried to ignore it, but she loved her big tits so much that she thought about it for the next hour, growing concerned. When Russ walked through the living room later, he didn't so much as glance at her boobs, which only made Tanya more nervous. If Russ loved boobs so much and he didn't look at them, was he right? Feeling self-conscious, Tanya got up and followed him to the kitchen.

"You really think they're smaller?" she blurted, drawing his attention.

"Definitely," Russ answered. "Sorry, but I used to have to make a concerted effort not to look at them. It's just biology, you know. Now, I hardly even notice they're there."

Tanya looked like she might cry. Russ put a hand on her shoulder.

"Hey, it's alright. Lots of women have small boobs. It's nothing to be ashamed of."

"But… I don't want to have small boobs!" Tanya blubbered.

"Okay. Look. The only way to know for sure is to check, right? We can just do a cockpillow test the next couple of days and measure the results."

"A what?" Tanya asked.

"A cockpillow test," Russ said again.

"What is that? That sounds gross."

"Gross? It's a perfectly sound, scientific test to measure spontaneous breast reduction," Russ explained, sounding offended.

"Is that a real thing?" Tanya asked.

"Of course," Russ said, shaking his head. "Look, which one of us is the engineering student here?"

"Um, you?"

"Right. You'd say I'm pretty smart, right?"

"Yeah," Tanya agreed.

"Alright, then I'll help," Russ said, not bothering to confirm in any way that Tanya wanted help.

Tanya, concerned and confused, nodded her head and said, "I… I guess that's okay. Shouldn't I go see, like, a doctor or something?"

Russ looked offended and horrified, saying, "Seriously? What are you going to tell the nurse when you make the appointment? That you're suffering from spontaneous breast reduction? Jesus! Can you imagine how embarrassing it would be? She'd probably tell everyone she knew, and they'd laugh at you over drinks. I mean, if my dick were shrinking, I sure wouldn't want anyone to know."

Tanya blushed and said, "I… I guess so. So, you can help me check?"

"Yeah. Let's go upstairs. Just, let's be quiet about this, alright? I know you don't want anyone knowing how flat-chested you're going to be in a few weeks."

Tanya looked terrified at the idea. She followed Russ up to his room, where he shut the door.

"Alright," he said seriously. "Go ahead and take off your top."

Tanya dithered, her fingers resting on the hem of the top.

"You're sure about this?" she asked.

"Absolutely. Unless you'd rather I call the doctor's office and tell them about your condition."

"No!" Tanya said.

She tugged her top up and over her large, ripe melons. Russ barely contained his glee, his erection, and his excitement behind the serious mask.

"Alright. Now, just lay on the bed," he instructed.

Tanya lay on the bed. Russ undid his belt and began to take off his pants.

"What are you doing?" Tanya hissed.

"Well, you can't do a cockpillow test without a cock. Duh?"

"You're sure there isn't a different way?"

"Sure, if you don't want accurate results. This is the only way to be sure. If you'd rather watch your boobs shrivel away into mosquito bites, I suppose that's an option."

"No! Okay," Tanya relented, blushing.

Russ tugged off his pants, his underwear, and approached his topless sister with his cock hard. Tanya's eyes followed it as he straddled her chest.

"Now, it's very simple," Russ explained. "I'm just going to put my cock between them, and we see if your boobs swallow up the entire length. We'll repeat the test each day, to check if there's any change."

"What if... what if they're getting smaller?" Tanya asked, frightened.

"There are a few methods we can try. A couple of them might stop the shrinkage altogether. Others might plump them right back up for you. Let's just test where you are first, alright?"

Tanya nodded. Russ steadied his hands with a few deep breaths and then placed them on his sister's large, firm tits. He pinched her nipples lightly and tugged on them, making Tanya yelp.

"Don't worry," Russ said. "I'm just getting the blood flowing for you. Okay. That looks good."

He pressed her tits together with his hands and then pushed the head of his cock between the valley of her titflesh. Goddammit! It was heaven. Carefully, he inserted just the first couple of inches and crushed her tits together around his shaft. Because of her large udders, Tanya could not see exactly how much cock there was left to go. As much as Russ wanted to roughly shove the entire length of it between those cockpillows, he held off for a bigger payoff.

"Can you see the other end of it?" he asked.

Tanya looked down at her cleavage and said, "No. Is that a good thing?"

"We won't know until we measure again tomorrow."

Reluctantly, he pulled his cock out, dismounted her chest, and put his underwear back on.

"That's it?" she asked.

"That's it. See? Not so bad. We'll do it again tomorrow and check the results."

"Alright."

***

The next day, when Tanya got home from school, she went to Russ's room and performed the test again. This time, Russ pushed a further inch of his cock between her tits and said, "Hard to tell, but I think they're definitely smaller this time. Can you see the other end of my cock poking out?"

"No," Tanya admitted, frightened.

"Alright. Let's check again tomorrow."

On the following day, another inch of his cock went between her melons, and another on the next day. By the fifth test, Tanya could see the head of her brother's cock poke from the mountains of her titflesh.

"Oh my God!" she exclaimed. "You're right! They're… they're getting smaller!"

Russ shook his head sadly and said, "I'm sorry, sis. I really am. You'll probably be flat-chested in a few weeks if you don't do something about it."

Tanya, her tits still wrapped around her brother's cock, and his hands squeezing them like toys, asked, "What can I do?"

Russ pretended to think about it as he gently rocked his cock back and forth through her tits, and then said, "Well, normally the first step is to lubricate them and perform a seminal injection."

"Injection?" Tanya balked. "I don't like needles!"

Russ shook his head and said, "No, not like that. Here. Let me show you."

Tanya, concerned, agreed. Russ released her melons and opened his nightstand, retrieving a bottle of jerk-off lube. He poured a bit of the stuff between Tanya's tits then set the bottle aside. Then, he placed his cock between her tits once more and pushed them together.

"Okay, now, I'm just going to stroke the length of it between them until we get a good coating of semen to rub into them. If we do this often enough, that should put a stop to the shrinkage," he explained.

"How… how long will that take?" Tanya asked.

"Well, I hate to tell you this, sis, but this isn't something that's going away. This is a lifelong condition. If you don't want your boobs to get smaller, you're going to have to do this pretty often."

Tanya sniffled and nodded. Russ pushed her tits together and stroked his lubricated penis between them. God, this was exactly what he'd been waiting for, and it was divine. His sister's huge melons swallowed up his cock. He squeezed them, tugged on her nipples, and crushed them in his hands as he jerked himself off. He was right. It didn't take long. Within a few minutes, he ejaculated onto her udders, coating them in spunk.

His immense, pent-up load sprayed across her nipples, onto her chest, and struck her neck, a few sprays even striking her lips. Tanya flinched but Russ kept his composure. He began to smear the sticky cum into her tits, scooping it up and making a show of carefully rubbing it into her globes, checking to make sure there was a nice, even coating.

"Alright," he said. "We're going to have to do this as often as possible and keep checking the results. Make sure you don't wash it off. Just let it dry for as long as you can before you shower. You should avoid wearing a top or a bra until you have to."

"Okay," Tanya said. "Thank you! What do we do if they keep getting smaller, though?"

"We'll cross that bridge when we come to it," Russ said, idly squeezing her tits. "If you're not seeing a return to your normal size in a few days, though, we'll probably have to move on to a direct, internal seminal injection."

"What… what does that mean?" Tanya asked.

"Let's not worry about that just yet," Russ said. "It can be oral, vaginal, or rectal, but one step at a time. Let's not be hasty here. I'll come get you when I have more helpful semen for you, alright?"

"Thank you so much!" Tanya said.

Of course, Tanya's tits continued to shrink. Russ, thankfully, had a solution to keep them just as large and bouncy as Tanya loved.