Okay, so maybe I do have a weird obsession with Phinabella sex scenes. Shoot me why don't you. Whatever. I randomly thought of this so I wrote it down (or typed it, you know what I mean). In this Phineas and Isabella are a couple (obviously), 18, living together, not married, and this isn't related to my other stories. I don't know what the hell my inspiration was, but here it is. It started out as a one-shot but I got a few ideas and now it's going to be an actual story. Enjoy!

Phineas was sitting in bed, reading a book, waiting for Isabella to come in so they could go to bed. The two of them had been living together for a few months now. They had gotten one of Phineas' inventions patented, and used the money to buy the apartment. It had been Phineas to suggest living together. When they were 14, Phineas had started picking up some of the hints that Isabella was dropping, and he finally came to the realization that she loved him. Of course he returned the feelings. How could he not?

A minute later Isabella walked in, her hair still slightly damp from the shower she had taken. She was dressed in a loose pink shirt and black pajama shorts. Phineas put down his book, smiling to her as she approached the bed.

"Just let me change quickly," she said, facing away from him and opening a drawer on her dresser that sat next to the bed. To Phineas' embarrassment, she started pulling her shirt up over her head. He must of made a sound because Isabella turned her head slightly, smiling.

"It's fine Phineas," she said. "No need to be shy."

That only sought to make him even more embarrassed, but he didn't turn around. She didn't have anything under the shirt, so Phineas saw the bare skin of her back, and found himself unable to look away. Isabella was looking through the drawers for something, and when she found it, she started pulling down her shorts. Phineas wasn't quite ready for that yet, so he turned his head away, blushing. He heard fabric being moved, but when it stopped, he still didn't turn around until he felt the bed move as Isabella lay down next to him. She giggled when she saw his head turned, so he turned back around to look at her, and was surprised by what he saw.

Normally, Isabella wore her black shorts and pink shirt to bed, but tonight she was wearing a white V-neck tank top with a very low cut, and a pair of black lace underwear. Phineas found himself almost speechless looking at her, and she laughed.

"Just thought I'd try something new tonight," she whispered seductively, moving herself closer to Phineas. His breathing became louder as she pressed herself up against him. She gave him a soft kiss, and that seemed to partially snap him out of his stupor.

"I-Isabella," he managed to get out. She raised an eyebrow, still smiling.

"Yes, Phineas?" she cooed, wrapping her arms around his neck.

"You look... wow," he said, unable to take his eyes off of her. She smiled wider, her eyes slightly narrowed. Her alluring expression made Phineas shiver, which Isabella felt pressed against him as she was.

"Why thank you Phineas," she replied, pulling him closer, and Phineas found himself once again speechless. Isabella giggled once again and took one of her hands from around his neck, running it along his bare chest. Phineas found his gaze drifting lower from her face, and felt his breathing speed up. Isabella noticed where he was now looking and blushed slightly, sliding her hand lower and stopping right above the waist line of his navy blue pajama shorts. She slowly slid her hand under the elastic, and then she felt Phineas' body stiffen. Her hand immediately stopped moving and she brought her eyes up to meet his.

"Do you want me to stop?" she asked quietly. Phineas squeezed his eyes shut and slowly relaxed, shaking his head.

"N-no, it's fine," he managed to get out, opening his eyes. Isabella smiled and started moving her hand down again. Phineas shivered once again at her touch, a bulge growing in his shorts. Suddenly she pulled her hand out and got up on her knees. Phineas looked at her curiously, his eyes widening as she gently pushed him down lower onto his back and crouched low over top of him, smiling mischievously. She lowered her head down to kiss him, crushing her lips against his, and then slowly moved her head down, kissing down his neck, his chest. Phineas let out a shuddering breathe the lower she got. When she got to his shorts she looked up at him, as if asking for permission to continue. He managed to nod, still in a state of shock. Isabella winked and brought her hands down, slowly sliding his shorts off. Since they were going to bed, he had nothing on underneath. Isabella kissed lower, trailing her tongue lightly over his erection.

Phineas' breathing was coming out in deep uneven gasps now as Isabella continued. Thoughts kept flickering into his head and he felt himself unable to ignore his urges anymore. He moaned quietly, and Isabella looked up, bring her head up to his to kiss him again. Phineas finally allowed himself to give in, and so, to Isabella's surprise, he put his hands on her hips and flipped her around so that he was now on top. She let out a small sound of surprise to find Phineas reacting more aggressively to her actions. And she loved it. He leaned down and kissed her hard, and with more passion than he ever had before. After a minute he pulled away, putting his hands on her shoulders and taking her tank-top straps in his hands. Isabella raised her eyebrows playfully, as if asking him what he going to do next. He answered by pulling them down until her tank-top was at her waist, and then he leaned down, kissing the valley between her breasts. She leaned her head back and closed her eyes.

She hadn't expected Phineas to take the initiative to go ahead himself, but she was most definitely not disappointed. Normally, he would be hesitant, although Isabella could always see it in his eyes that he wanted to continue. He was simply afraid. Afraid of what, she couldn't imagine, so she let him take his sweet time. She never pushed him farther than he was ready. But tonight, she simply couldn't resist. Of course, if he had asked her to stop she would have, but Isabella could see that he was finally letting himself go.

Isabella sighed in bliss as Phineas brought his head up and started kissing her neck, his hands trailing over her soft skin. She grinded her hips up against his, hoping he would get the message. He stopped kissing her and lifted his head up, looking deep into her eyes, a nervous expression on his face, which he was doing a very bad job of hiding.

"I don't know Isabella," he said nervously. "We're not even married yet."

"Does it matter?" she inquired, tilting her head slightly.

"I guess not, but what if you get, y'know."

Isabella smiled gently, knowing what he was referring to.

"Don't worry about it, I've been on birth control for a while now," she told him. Phineas nodded slowly, still not making a move to continue. Isabella put her arms around his neck again, pulling him close so that their foreheads touched.

"Phineas, I love you, and I know that you love me too. So what have we got to lose?"

After a moment he nodded again, so Isabella smiled seductively and pulled him in for another kiss. Instead of pulling away, Phineas deepened the kiss, moving his hands down her body to her hips, where her tank top still rested around her waist. He hooked his fingers onto that, as well as her underwear, and slowly slid them down, making Isabella kiss him harder. She kicked them off when they got to her knees, her heart racing a million miles an hour. Her fingers traced teasingly over his waist, just high enough to not touch anything, but just low enough to make him beg for more. Phineas slid his hand down her stomach, grabbing her hand and holding it close. Time seemed to freeze as they lay there, kissing each other like it was the only way to survive.

And then Phineas took the final step, bring them closer to each other then they had ever been before.

So, what did you think of the first chapter? About half way through I had a random shot of inspiration, and after thinking about it for a while, I decided that I would continue on from here. I'd love to hear what you thought.