Full summary: (since this site won't allow long summaries)

For years, Phineas and Ferb have built inventions, their sister Candace has tried to bust them, their neighbor Isabella has tried to flirt with Phineas, and Phineas has been living in blissful ignorance of both. But when Jeremy leaves for college, when Candace freaks out over that and becomes even more insecure than before, when Ferb figures out just why Phineas cares so much about his sister's behavior, when Vanessa Doofenshmirtz's new college buddy implies that her father's old nemesis is in fact his girlfriend's brothers' pet, when Isabella decides she could get her crush's brother to help her as her new confidant and wingman, when emotions reach their breaking point and feelings become more confused than ever, and when absolutely no one is being open and honest with each other anymore...

...that is when what has been a stable situation for years suddenly descends into complete chaos, as no one is quite sure what feelings, relationships and friendships will survive the mess.

Disclaimer: Phineas and Ferb, including all characters and their inner thoughts and feelings, belong to either Dan Povenmire and Jeff "Swampy" Marsh, to themselves in their own distant dimension somewhere out there in the multiverse, or to both. I can not and will not claim ownership to them.

Author's Note: Okay, so this is a long fanfic, and people might want to check out my other story, "The Shrunken Sister", before reading this if only to look at the Author's Note which explains some more about the pairing involved and my view of the characters, even if both stories can be read separately. For now, I'll stick to the following:

This is a story which aims to achieve two of the most difficult pairings in the Phineas and Ferb fandom, Phindace and Ferbella. The latter is well-known on this site and around the internet, but when executed in a story often features versions of Ferb and Isabella who are already good friends. Ferb, in such a scenario, is Isabella's longstanding confidant and therefore Isabella's feelings towards him simply change from close friendship to romance. While there are many impressive fanfics written from that starting point, I've always thought it was iffy to not show such a clear change from the show (where Ferb and Isabella have little on-screen interaction) in the actual fanfic itself. Although Ferbella isn't the primary focus in this story it is an important subplot in its own right, and in that subplot I attempted to address these issues at least to some degree.

And then there's Phindace.

We all know Phineas cares deeply about Candace. We also know he's sung a love song (Gitchie Gitchie Goo) with her and that he builds as much for her as for anyone else, despite her behavior towards him being downright hostile at times. We know that despite everything Candace does not hate her brothers and does, in fact, rely on Phineas for help in case of emergencies - he's almost always the first person she turns to, and as shown in Summer Belongs To You and in Phineas and Ferb Save Summer, his track record of helping her get out of depressions is fairly impressive. He also provides a stable, optimistic, laidback balance to Candace's neurotic, paranoid behavior, and of all characters in the show, he is best equipped to handle her flaws, flaws he comes into contact with much more than Jeremy does, but which have rarely ever deterred him.

But all those observations are academic as long as Phineas remains an oblivious inventor and Candace's mind remains geared to two tracks, namely busting her brothers and romancing Jeremy. But those two facts are utterly dependent on the status quo. A status quo that can quite easily be shaken up by one character leaving Danville and going to school somewhere else - as indeed happens in the episode "Act Your Age". In fact, apart from the ridiculous ages that episode implies Phineas and Ferb are in the present, this story can and does fit into the background of Act Your Age.

Only with the one important divergence that happens when Phineas is 13 years old (one year before he would have gone to high school in AYA and would have come up with the idea that he had a crush on Isabella) and steers his romantic future into another direction, leaving feelings that might have otherwise remained hidden under the surface to roam free. And that is what turns not just Phineas' life but also that of Candace, Jeremy, Ferb, Isabella and many others from relative stability into abrupt chaos.

To Phineas Andrew Flynn, the moment he first met his future girlfriend – his 'soul mate', the 'love of his life', as people with more romantically inclined minds than his own would have called it – came when he was only three hours old.

Although he was only just born, his intellect and curiosity were already working well enough for him to take in and try to make sense of everything around him. This was mostly just the sky, as his mother had him wrapped tightly in a bundle from which he could only look up, but it was enough to leave him amazed.

Then the environment changed as they went into a house, and he was only just getting used to this when he became aware of his mother handing him over to someone else on a lower level. Tiny hands wrapped around him.

Phineas curiously looked up to see what was happening to him. When he did so, he saw a little girl with orange hair, who was looking at him with as much wonder as he was at her. When she saw what he looked like, though, her face contorted and she looked… disappointed. Somewhat confused. As if she had been expecting something or someone else.

But Phineas Flynn wasn't going to let that hurt him. Instead, he tried to cheer the girl up in the only way he knew thus far: he smiled at her.

And then, after a moment of tension, she broadly smiled back at him.

They smiled at each other for about ten seconds, and when his mother tried to take him back from her, the girl pouted. "Can I hold Finny-as, mommy?" she asked.

Their mother smiled. "All right, Candy" she replied. "Why don't you carry your little brother to the couch. But be real careful with him."

Candace beamed, and nodded eagerly. She held little Phineas close to her chest and carried him over to the couch, where she settled in and put the baby on her lap, not taking her eyes off him until well in the evening.

Candace being intrigued by her little brother lasted about as long as it took for her to find out that he slept half the day, occasionally cried, and was frankly useless as a playmate. But as little Phineas grew older and learned to crawl across the floor, he and Candace became inseparable. Candace doted on her baby brother, who could make life fun simply by being happy at everything he did and thus was the one to cheer her up even when life was dreary (well, him and Ducky Momo). Phineas in the meantime looked up to his big sister immensely, following her everywhere and trying to do everything she did as well – which went completely wrong sometimes, but that never stopped him from trying again the next time.

It was only as they really grew older, when Candace befriended Stacy and Phineas gained a stepbrother in Ferb and friends in Isabella, Buford and Baljeet, that they grew apart, which was more Candace's doing than Phineas'. And by the time Candace regained her interest in what her little brother was doing, her sole intent seemed to be to get him punished by their mother for his impossible deeds. Jealousy and obsession consumed her, undermining the good relationship between them which still existed in spite of everything.

Phineas, on the other hand, didn't really change from how he was as a newborn and continued to look up to his sister, which made him try to involve her in his projects every chance he got. His exact feelings towards her did change over time, developing from a fraternal fascination into an interest that was more than just brotherly and gradually started to take on the contours of a crush, which in the meantime made him oblivious to anybody else showing similar affection to him.

But given Phineas' clueless, optimistic and generally a-romantic nature, those feelings lingered under the surface, while Candace on her part continued to see him as nothing more than her sweet, sometimes annoying little brother. It wasn't until that fateful autumn of 2012, when suddenly everything in their lives started to change.

oooooooo

To Ferbs Fletcher, his stepbrother, best friend and partner-in-life in every sense but the romantic one (even if some gossip magazines would beg to disagree on that last part), the moment of first meeting the girl of his dreams came at a wholly different stage in life.

He had only just moved into the United States with his father, to whom he stuck closely as they travelled around the country, trying to find a place to settle. It was in Danville where his father met the woman who could heal the hole in his heart Ferb's mother had dug there, and it was there that Ferb had met his future brother and sister. His brother Phineas was a cheerful and talkative boy whom Ferb instantly took a liking to, and who took it on himself from the start to understand what Ferb meant even when he remained silent, with varying degrees of success.

It was on the third day after their first meeting that Phineas, who had shown him everything inside the house already, decided it was time for them to play in the backyard, and Ferb happily went along. Phineas showed him the sandbox, the trees and the gate, mundane every-day-items that nevertheless became exciting because of the way Phineas talked about them. He was already figuring out what they could do with them and considered proposing to modify the tools in the sandbox when the garden gate swung open and a pretty girl with a pink dress, black hair and a hair bow walked in.

"What'cha doin'?"

"Hi, Isabella," Phineas greeted her, "I'm showing my new brother around the yard! Now, the three of us will be able to play together."

Isabella looked at Ferb, who noticed that she had been looking at Phineas with a strange smile on her face that was gone when she turned to him. "Hi, I'm Isabella," she greeted him. "Who are you?"

"I'm Ferb" Ferb replied softly.

Isabella blinked. "You talk funny" she said. "In a good way though."

Ferb blinked at her, and after a few moments, a puzzled Isabella turned back to Phineas. "So, what'cha doin' today?"

Those first moments of their relationship established a pattern that would be there for the next nine years. Isabella would pay attention to Phineas but always ignore Ferb, even when she didn't mean to. For the longest time, Ferb didn't mind that. He found out quickly about Isabella's crush on his brother, explaining the discrepancy in attention they got from her, and he acknowledged and accepted that his silent ways made most of the other kids feel awkward about talking to him. The fact that Isabella liked Phineas didn't personally affect him, and even though occasionally he would find it annoying that Isabella was taking Phineas away from him, he never really developed a romantic interest in her besides considering her pretty in general. His primary romantic interests lay elsewhere, with a charming adolescent woman named Vanessa Doofenshmirtz, a crush which, despite acknowledging that it was a long-shot, he maintained for several years.

But that, too, would all change in the autumn of 2012.

Author's Note: This is the characters' first meeting - perhaps obviously, there is going to be a timeskip later on. Final observation (for now) is that this story won't contain Phineas, Ferb, Candace or anyone who doesn't know already finding out that Perry is a secret agent. Anyone hunting for stories based primarily on that premise will be disappointed. I did originally toy with that idea and that may be why there appears to be some foreshadowing here and there, but it's not going to happen since it would make the situation even more complicated, and this story is already going to be complex enough.

Also, Ferbs is Ferb's canon full first name as confirmed by a tweet from Dan Povenmire last year, so I didn't pull that out of thin air. Even if it sounds wacky enough to make me wonder if I did sometimes.