Jake and Mom stare as Jenny starts to change. Nothing seemed to be happening, until suddenly Jenny moaned. Jake and Mom watch as the changes start to roll over her body. First she grew taller, climbing to about 5'8 or maybe 5'10. Her head lolled back as she moaned again, almost orgasmicly, arms extending, stretching longer as did her legs. Her shoulders widened along with her hips, accentuated with a loud popping sound. Another moan, this one deeper, almost primal, shook Mom and Jake both in their very being, causing specific reactions to both of them.
"Oh no, Jenny! Are you ok?" Mom asked, panic in her voice.
"Mom?" Jake questioned, with no idea what was happening to his sister or himself.
Suddenly, Jenny's eyes snapped open, as she let out a deep growl, her changes speeding up, Clenching her teeth as her breathing became harsh, in short choppy segments, like she was working out very intensely.
Her eyes turned a vibrant shade of blue, so blue it looked fake or even inhuman. Her hair shifted from her natural red to shiny blonde, full of body and vitality. Her face sharpened and matured, looking like a late teen to early 20 year old, an unearthly aspect shaping her features.
"Oh...wow." Jake moaned softly, as his young body involuntarily reacts as he watches his sister's transformation continue, unable to control himself.
"Oh..my." whispers mom, her own control waning as she witnesses the medallions work. Hands slipping between her legs as the both watch the changes continue.
Jenny's body suddenly expands, like a balloon inflating, building on her already athletic form from years of soccer. Her shoulders round out and thicken, biceps and triceps add layers of muscle, growing tighter and rounding out, firming up into balls of power. Her neck bulges ever so slightly as her traps form up. Her pecs develop, inching out, becoming a chest plate while her breasts form into maturity, to the size of grapefruits, blowing out her now too small shirt, leaving it in tatters and rags hanging from her. The line from her pecs travels down to her abs and turns her flat tummy into a cobblestone road of 6 bricks of muscles as her obliques form and pulse. Her thighs, already large from her sports life, solidify into tree trunks, exuding power, while her calves form diamond heart shapes and shred her socks. Her feet grow slightly but quickly, blowing out her sandals. Jenny looks down at her brother and mother who are about 6 inches shorter than her now and smiles mischievously.
Jake and their mom look up at the new Jenny with their mouths hanging open. Then they gasp as it looks Jenny starts to get taller again. Until.they see her feet travel into view. She floats up to the ceiling and giggles. "Wow. That was good, but this is amaz..ugh." she starts to say and then double over in pain still floating in the air. Slowly she descends and lays on the floor, her mom right there when she settles, Jake unable to approach. Jenny let's out a soft grunt and then a tearing sound can be heard. Mom gasps as she looks towards.Jenny's crotch and witnesses the last piece if the change as her little girl underwear now sits on the head of a very impressive and firm penis.
Jenny moans in a combination pain and pleasure and rolls over onto her knees to ease the sensations when she digs a furrow into the floor, without even flinching.
"Jake! Give me the underwear!" Mom cries, trying to figure out what to do.
Jake moves in stunned and awkward slowness, handing the underwear that caused this to her. His discomfort is very apparent as the changes to his sister finish taking hold.
"mom..you need to move. Please." Jenny whispers, a sense of urgency and fear in her whispered voice.
Her mom hands her the underwear and complies Before she even realizes she let go of the garment, Super Jenny is gone, wind twirling around her, as a sound behind her breaks her out of her trance. She turns and sees Jake, shuddering, a wet spot forming on his pants and look of both relief and horror on his face.
He looks at her as tears falls down his face, lip trembling. "I'm sorry. I didn't mean to..I couldn't control it." Mom moves to him and hugs him tight. "It's ok. This had been all sorts of weird. I just hope Jenny's ok."
Suddenly a loud whoop of excitement and enjoyment can be heard passing by the house. Mom and Jake look at each other, uncertainty on their faces, then they head outside to see what is happening.