The dictaphone

"Eeeer... Chelsea, are you okay?" Cassidy wondered, looking at the weird way her friend acted.

"I need to take off this ring! It's stuck!" Chelsea grunted while still trying to get rid of the ring.
"You need to? What's wrong with it? It looks good." the girl said.
"It's because it just... it just..." Chelsea calmed down for a moment. She focused on breathing slowly, until she was once again able to think clearly. She looked up at Cassidy, who was still gazing at her like she was crazy. This wasn't going to be easy.

"Okay Cassidy, I need you to trust me because it will sound crazy. Swear you'll trust me, because it's the truth. Okay?"
"Okay, I swear. I trust you, Chelsea."
"Alright. While you were looking at phones, I noticed a new shop in the mall, just facing the one you were in. Looked like a shop full of fake magic items. The girl inside offered me a free sample to prove me the stuff was real. I took this ring, and... okay, this is downright ridiculous. The ring is supposed to enlarge a girl's chest each time she desires to be bigger."
"Why would you..." started Cassidy, immediately stopped by her friend.
"I didn't believe her, of course! I just wanted to outsmart her by taking what looked the most expensive as a free sample! This ring looked worth something, since it's made of gold. But earlier, I was a B cup. I searched for a bra, found a nice one only available in C cup size, and since I was disappointed, boom! These enlarged suddenly until I was a C cup! And my bra changed too! And neither you nor the clerk noticed anything! It's like I always was..."
"A C cup." Cassidy calmly said "And yes, you definitely sound crazy. So here are our options if I am to believe you : or the girl at the shop managed to drug you somehow, through the ring or through vapes in the shop... ooor you're wearing a magic ring magically growing breasts and adapting reality to your new tits anytime you want to grow bigger. Is that it?"
"I think I'd prefer the drug stuff." Chelsea said "Please, make it so it was the drug stuff!"

She left the shop quickly, followed by Cassidy.

"Wait! Where are you going?"
"Back to the shop they gave me this! They'll give me an answer, one way or the other, and help me get rid of this!"

She quickly ran in the mall, until she was where she found the shop.

But of course, the shop wasn't there. In fact, there wasn't even space for a shop there. The two other ones that used to be on each side of it were now touching. It was...

"... impossible." whispered Chelsea.
"What? The shop was there and now isn't?" Cassidy said.
"How do you know?!" Chelsea exclaimed.
"Easy: if it's not the drug option, it's the magic option."
"You mean... you believe me?" Chelsea asked, surprised.
"Not totally, I have to admit it. But I never saw you this serious before when you asked me to trust you. So I try my best there. But sure, to me, you've always had a larger chest than I do. And it's been years. Not that I look much at your chest, though. But nevermind : if you don't want a bigger chest, you're safe, right? And you're not the kind of girl to desire one."
"Yes. Yes, exactly. The first time was an accident. I don't want bigger breasts."

"Too bad, because there's only one way to know you say the truth..." Cassidy said.
"What? What do you mean?" Chelsea was quite shocked by how she said "Too bad" about all this!
"I mean" the girl said with her usual, cool tone "You changed in front of the clerk in the shop. And she didn't know about the ring, and neither did you. Maybe that now that I know, and if it were to happen in front of me, I might be able to witness it..."
"No!" Chelsea exclaimed "Chelsea, that's not a game where you press buttons! It's... my body, and I don't want to grow bigger!"
"But look." Chelsea took her phone, and opened a new message. She typed "Chelsea has always been a C cup". And sent it to Chelsea. "Now, we both have the same message indicating your cup size. Maybe one of the messages won't change when you grow, so I'll have my proof, even if my memories are altered or whatever!"
"Cassidy, no! I don't wanna grow, is that clear? Just... trust me!" Chelsea said.
"Come on, it's for science!" Cassidy said, amused "And I don't totally believe all this yet, so let me at last..."
"No, no, and no!" Chelsea covered her chest "No!"
"I'm sure I can make you groooow!" giggled Cassidy, amused by her friend's attitude.
"No you won't!" Chelsea started to walk away, but Cassidy was following her quite closely.
"Chelsea, pleaaase, just once! Show me! Think about big D cups!"
"No, no, no, not interested!"
"Big beautiful D cups bouncing on your chest, so boys look at you!" Cassidy giggled even louder.
"Noooo, please noooo!" Chelsea walked faster, hands over her C cup breasts bouncing more than she wanted to.
"Come on Chelsea, grow to D cup for me! You know you want them!"

Chelsea was focusing on thinking about anything but owning a bigger pair of breasts. But with Cassidy behind her saying these things... it was getting harder. But then, Cassidy added :

"You know you wanna increase the gape with me even more with a larger chest making you look older!"

It lasted the time of a single thought. Yes, for a millisecond, Chelsea thought a bigger chest would make her look older, which would be a good thing, and yes, Cassidy would shut up if she was in a totally different league.

She stopped right there as she heard the sound of her breasts filling up like balloons, and could feel the band of her bra moving as her breasts expanded larger, and her cup soon followed the move. She gasped, and looked down to meet two healthy D cups stressing her shirt. She turned to face Cassidy, furious.

"Cassidy! What have you done!" she exclaimed "Look at me!" she hefted her D cups, and a few people walking by got a good look.
"Let me check my phone..." Cassidy said. She then showed the message to Chelsea : "Chelsea has always been a D cup". Even the message had changed! Chelsea checked her own phone in panic, and confirmed it : her message had changed too. There was no trace she had ever been a C cup. And even less of her original B cups.
"So?" Cassidy asked "Nothing happened."
"I GREW!" shouted Chelsea before she noticed the people looking at her. Maybe the mall wasn't the best place to talk about all this.
"If you did, sorry but I didn't notice, Chelsea. You're still sporting your stupid D cups."
"Stupid?!" Chelsea said, a bit annoyed to have Cassidy talk about her body this way.
"Come on, you know I don't like how you use these to look older or get some attention sometimes. But yes, it's still totally like you to get some breast growth ring to go even bigger. You don't know when to stop."
"Cassidy, no... no, wait, I was a B cup! And YOU made me grow just right now!"

"You'd love that for sure!" Cassidy shook her head "Geez, I don't even know why I agreed to believe a bit into your stupid breasts expansion story. I'm sure you just love to make me talk about your big balloons."

"Hey, no!" Chelsea was shocked by her change in attitude. Did the reality change affected... their friendship?

"Cassidy... believe me... I beg you..." quietly begged Chelsea, looking at her friends in the eyes...