Mary suddenly felt odd. Her tail started getting longer as her "thighs," for lack of a better term, widened. "Aunt Carol!?" She said in a worried tone. Mary felt her fingernails grow and become the same blue as her tail. Her waist narrowed and she felt her breasts expand. She clasped and kneaded them, moaning sensuously as her hair cascaded down her back.
Carol watched as her niece's youthful, teenage looks gave way to a gorgeous mature woman; right around Carol's own age. Mary crawled over to her aunt and hugged her as Carol stroked her long, full hair. Their bare breasts were pressing up against each other. "Carol!" Mary said in a mature, sensual voice that would turn any head. "What just happened to me?"
"I'm not sure." Carol answered. "Maybe mermaids mature quicker than humans? Who knows how their biology works?"
"Oh, I'm not complaining. I LOVE this!" Mary said, giving her aunt a tight hug. "I'm finally as gorgeous as you!"
"You... think I'm gorgeous?"
"Since I was 13, I wanted a body like yours; voluptuous, sexy; the kind that turned heads, even women's!"
"I didn't know you felt that way about me." The compliments about her beauty, combined with the contact of their breasts, were causing Aunt Carol to develop... ideas.