Ring, legendary (unique)
100 gp
A simple gold band with a large round stone atop it, wit a smaller round stone inset into the center of the first stone.
When worn by any creature, the Ring of Mammarius becomes attuned to them and can not be removed unless a Remove Curse spell is cast. Upon being worn, the larger stone changes color to match the wearer's skin tone, while the smaller tone matches the wearer's mucus membrane tissues.
As a free action, the creature wearing the Ring of Mammarius may twist the stones in place. Rotating the stone one notch clockwise results in the creature growing one cup size larger breasts even if they normally wouldn't have any. Rotating the stone counterclockwise reduces their breasts by the same amount, no more than leaving them flat chested. Any creature within five feet of the ring may attempt to make the action with a DC 15 Sleight of Hand.
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Jamie looked down at the ring attached to her finger. Attached, because no matter how much she tugged or used dish soap it seemed unwilling to come off. She sighed, looking at it in the sunlight streaming through her kitchen window. It was a beautiful ring with large priceless stones that would be worth a fortune, if it didn't look like a mineralized breast on her finger.
She fidgeted with the ring one more time, regretting finding it at that antique shop with the strange old man. She felt the ring click, and she gasped, a sudden tightness in her chest.
Was she poisoned? Did the ring inject something into her? Fruitlessly, Jamie held her breath. Moments passed, and she finally exhaled. Whatever happened, she wasn't dead. Her chest still felt tight, but other than that she was fine.
Carefully, more methodically, Jamie investigated the ring again. The stone seemed loose, and willing to twist in it's socket. With a small click, Jamie twisted it clockwise, and gasped as her breath was taken from her.
She looked down at her top, her breasts spilling out over the edge of her strained bra and pushing against her t-shirt, damp from her earlier splashing at the sink. Glancing out the window, Jamie striped off her shirt and under garment, looking at her bare chests.
Were they bigger? They felt heavier, but it could have just been her imagination. Gritting her teeth, Jamie practically spun the ring, twisting it for multiple clicks at once. With a yelp, her balance shifted forward as more mass magically appeared on her chest. At the start of the day, she had barely been an A cup, but now she had to be at least a DDD. She cupped the massive orbs gingerly in her fingers and shuddered. They felt so good, and more sensitive than before. Her nipples stood rock hard, poking out from her chest for the first time in her life and brushing against her palm.
Her roommate, Sally, had been watching the production for a few moments, sneakily getting close to her friend. It was clear the ring was doing this, but not much made more sense than that. Suddenly Sally grabbed Jamie's hand, and with a sharp "Ha!" twisted the stones around multiple times
Jamie gasped, falling forward into the sink. She moaned out lewdly, at a loss for words as her breasts quickly filled - and then overflowed - the sink in front of her. It was all she could do to stand up again, but the motion sent her careening onto her backside.
"What… what did you do that for!" Jamie exclaimed.
"Saw you having fun, wanted to share. Geez how big are you?"
Jamie looked down at herself, shaking her head. "Uhh...well, how big is 'I can't hold one of them even with both hands'?"
Sally laughed. "Honey, I don't think all four of our hands could hold those babies up. Say, wanna share that ring, I have a dress I could fill out."
"Can't. It's stuck."
"Dang. Well, at least we can have some fun."
Jamie looked mildly panicked looking at the ring as best she could with two watermelon sized globes on her chest. "What if I'm stuck like this?"
"Nonsense, there has to be a way to change you back. What if you spun the ring the other way?"
Jamie thought for a second before doing so, relieved to feel her chest getting lighter by the second. She stopped back at her DDD cup stature though, grinning at Sally. "Say… we were both staying in tonight anyway… wanna see how big these can get?"
Before Sally could answer Jamie twisted the ring multiple times, repeatedly growing her chest until it was so large that her arms were forced apart and she couldn't use the ring anymore. "Uh oh… help?" Her meek voice called out from below the piles of flesh.
Sally grinned wickedly, shaking her head. "Nuh uh. Not until I do some tests of my own~"