Erika stepped into her one piece swimsuit and pulled it up, anxious. It was simple in shape, black with a racerback and large white vertical stripes on either side of the body. The suit was stretchy enough to fit, and she hoped it would not rid up her butt too much once in the pool... Fortunately, the little patch of fur on her groin was not visible through the fabric, and neither was her happy button. Her breasts felt heavier than when she woke up earlier, though.
She was interrupted in her self-examination as her classmates were entering the lockers room to change clothes. Erika found herself looking at them, comparing her new shapes to theirs . Most still were early in their puberty, but a few had gone through quite the growth spurt and looked more mature. Her friend Melissa in particular was an early bloomer, and looked pretty self-conscious as she stuffed her C cups into her suit.
Erika felt very hot and realized her own nipples were showing through her swimsuit; she rushed to the showers, letting the cold water run over her body for a minute. From what she could tell, her clitoris seemed to be taking the hint, receding somewhat into its hood. After that, she joined her classmates in the pool and followed her PE teacher's instructions.
She found herself quite energetic and actually enjoying the water more than usual, but her mind kept wandering off to what had happened in the lockers room; it was like looking at her friend's body was precipitating the strange warmth in her own, and Erika being a bit naive and inexperienced, she didn't understand why that was.
An uncomfortable stir between her leg sent a shiver of panic through her mind. Erika was trying her best to keep her composure and do her swimming laps, but she was pretty sure the thing on her groin was swelling! She kept swimming, breathing deeply to keep calm, but the fabric was rubbing more and more against her expending nub. She gave a light brush with her hand to check and found a little bump had appeared, and seemed to harden under her touch.
She needed to get out of the swimming pool before the situation could get worse. She swam to the edge of the pool to call her teacher, keeping her body against the border to block the view.
"M. Parker, I don't feel so good! I think I need to use the loo..." she pleaded from the water. Her breasts pressed against the tiles, she could tell they had grown larger too, and her teats were slowly forming.
"Do you think it's serious, Erika? The course is almost over, perhaps it can wait a little longer" M. Parker replied.
Erika could feel her mutant clitoris poking further out in her suit. She pressed herself against the tiles but it only made it more erect underwater, slowly taking on a more canine appearance. As the hood turned into a sheath and directed itself vertically along her body, the bulge became temporarily less prominent.
"Yes! I... I think it's my periods, I really need to go!" Erika begged.