Disclaimer: Don't Phineas and Ferb in any way.

Rating: T

Pretty much what my summary said. Now you can read :)

Like she'd done many times before, Isabella opened the backyard door, walking in with a smile. "Hi Phineas, whatcha doin'?" she said, trying to be as cute as possible.

Phineas merely looked up, with his usual confidence and smile. "Oh hey, Isabella" he said, waving. "Ferb and I are just building a Growth Synthesizer, so we can make grass grow all the way to the sky"

True to his words, there was a massive field right by their house that hadn't been there before. It held a lot of normal-sized grass just waiting to be hit by their Growth Synthesizer machine.

"And then what?" she asked, stepping closer.

"Then we can climb up it, twist it into grass houses, make slides that gently deposit us on the ground" he said, counting off of his fingers, then he chuckled. "You know, have fun"

"I don't know, it sounds lame" Buford announced, walking into their backyard, Baljeet just beside him. "But it would be interesting to see how small we are compared to grass" Baljeet said.

This got a little 'argument' started between them in the background, while Isabella held her hands behind her back. "Definitely sounds like fun" she said. "Is it ready?"

"Let's see" he said simply, pushing the big red button on it.

The machine hummed and made noises, but nothing happened and they faded away.

He hummed, then looked up at her brother. "Ferb?" he called up to his brother.

Ferb simply put a finger to his mouth in thought, then he simply bungee-jumped off the top of the thing, multiple times as he checked across it's circuits. On the fourth jump though, he made a small tweak to a nut at the bottom.

The machine hummed to life, on and ready to be fired.

"Nice job, bro!" Phineas called up to him, getting a thumbs up from Ferb, 'Ding' sound effect included. Then he looked at Isabella, still smiling. "Now it's ready"

"Cool" she answered, but just after she said so, Baljeet was thrown past her. He hit another button on the curcuits.

The machine started shaking, it's curcuits humming louder than ever, then it started sparking.

"Hmm" Phineas said, looking at it. "That can't be good" he said, glancing at her.

The Growth Synthesizer machine start firing rapidly, the business end moving about willy-nilly. The kids ran for cover with screams, trying to avoid it's blasts (who knows what it could do on humans after all?). As it's blasts hit, it made grass grow so high you couldn't tell where the top of it was. They didn't see what happened to anything else it hit.

Phineas managed to duck behind the house's corner; Buford grabbed Baljeet and got outside the fence; Isabella kept dodge-rolling, but then she got trapped in a corner, making her scream as it turned toward her.

ZAP!

Isabella slowly became aware that she was completely fine. Blinking, she lowered her hands, looking over herself... she looked completely fine. And just after she did so, she heard the machine power down, then start smoking... Ferb's work.

She made a small sound, then she called out: "Guys! Ferb turned it off! It's okay now!"

Phineas peeked out from the corner, then smiled. "Ferb, good job!" he called up there, then he hummed as he tore open multiple panels on the bottom. "I really think we should get rid of that button, or maybe just rewire it so it can't do that anymore, and keep the button for show"

"Maybe I can help rewire?" Baljeet asked, still being carried by Buford. Having gotten permission, Baljeet looked up at Buford, who sighed and let him go, though he did keep a close eye on him.

Isabella was about to do the same, but she slowly noticed something seemed... off. It was subtle, but it was there.

She gave herself a full look-over, but she couldn't figure it out yet. Then she did:

Her white shirt sleeves were a quarter-of-an-inch higher up her arms, and her skirt was slightly higher than it had been. It might not have seemed like much, but it was noticable to her. She was either shrinking or growing... the latter most likely, all things considered.

She looked around quickly, but none of the boys had noticed yet. She almost gasped when she felt her clothing moving upward more on it's own! She WAS growing!

"This can't be happening!" she thought, slowly retreating toward the tree, increasingly worried. If she kept growing like this, she'd be too big for her clothes... and she did NOT want Phineas (or the other boys) to see her like that!

By this time, her clothes were starting to get a little tight, and somewhat in her chest (which was growing outward). But worse, her skirt was starting to slide up her hips!

She glanced around the tree: no one had noticed her yet. Looking around in fear, she quickly climbed up the tree, hiding herself as she watched herself continue to grow.

Down below, Phineas stood up, smiling. "All right, that should do it" he said, not noticing Isabella quickly jumping and landing on his house silently in the background, disappearing on the other side.

"Still lame" Buford said, taking Baljeet back into his holding position.

"Now, we just need to-" he said, trailing off when he noticed the backyard missing one person. "Hey, where's Isabella?"

Isabella panted slightly, having leapt from roof to roof. No one had seen her, but at least she'd finally stopped growing!

She no longer had the body of a ten-year-old (or whatever age she was supposed to be). Instead, now her figure was hourglass, and her legs gone from straight to normal. She'd grown twice her normal height, much to her embarrassment (her dress no longer fit, AT ALL), and she was just barely concealing herself as was. And instead of flat, she'd gained a chest, comparable to Candace's (future, that is).

She'd have to ask Phineas and Ferb to change her back... she'd need to.

But only after two things first.

Quickly taking out her cellphone, she called her troop, telling them to bring their sewing machines and measuring tapes. And quickly too, saying she was on the roof of her house...

That was step one.

An hour later

Isabella stood in front of her mirror, looking herself over carefully. This was step two.

She was wearing a considerably larger version of her normal outfit (ALL of it), suited to her new curves. She held the bow in her hands... because on this 16-year body (she guessed it was that age), it just didn't look quite right. Plus, she could always readjust it when Phineas and Ferb changed her back.

Speaking of them, she really should head over there... sure, she'd sent her Fireside Girls Troop to tell them about what happened, and tell them to make something to change her back... but the curiousity involved with her future looks/body was too great to ignore.

"I'm even cuter than before" she said to herself, smiling. "Though I wonder how I'll feel about these..."

She glanced down at her chest, slowly poking them once.

She resolved that she wouldn't know, and didn't need to know, until she was older. So after one last good look at herself, she turned and left, heading for Phineas's house.

She got there quickly, opening the backyard door easily, seeing the boys and her troop gathered around an entirely different machine.

"So ladies, this machine will reverse any effects from our Growth Synthesizer, and return them back to their normal selves" Phineas was explaining, not noticing her yet.

During this speech though, her shadow fell over Ferb, who turned. He blinked once, glancing up and down her body discreetly, then up at her face. He quickly patted his stepbrother's shoulder several times.

Phineas turned around, looking up at her. "Woah, Isabella" he said, sounding slightly stunned. "I had no idea our Growth Synthesizer could do to you"

"Well, I'll be okay if you change me back" she said, then she tilted her head, smiling. "But first, do you think I'm cuter?"

"Do I think you're cuter?" Phineas repeated, then he smiled. "Isabella, you're so cute, even I couldn't make a cute tracker that could take your cuteness"

Isabella looked at the fourth wall, her look pure -_-

Oh sure, NOW he noticed she was cute... and only on her older body.

She sighed, looking back. "Just change me back" she said bluntly.

"All right" he said, like nothing happened. Then he pushed a button.

ZAP!

She glanced down at herself; she was still in her older body. Maybe it was like the Growth Synthesizer... didn't work right away.

She sighed again, walking toward the house. "I'll be inside" she said, taking her normal-sized clothes from her troop first. "I'll be out when I'm back to normal"

"See you then" Phineas said, then he looked at Ferb. "What did you think, Ferb?" he asked simply, refering to Isabella's older body, but only honestly curious about his brother's opinion.

Ferb glanced toward the house, then he simply got a look. "Rrrrowr!"

Phineas merely stared at him in confusion, as did Buford and Baljeet.

*enter show's ending noise here*

And this oneshot is done :) I got the idea from a DeviantArt I saw about Isabella, made by ThetaSigma2010, which inspired this oneshot. It's mildly NSFW, just a fair warning (emphasis on mildly).

Hope you all enjoyed it. Leave a review.