Trigger warning: bullying
The initial impetus for this crossover was a mental comparison of Isabella's speech to Phineas at the end of "Summer Belongs To You" and Helen's speech to Dave at the end of the "Madness" storyline.
Many, many thanks to Shaenon Garrity for her help with Narbonic canon. Assume any errors in canon are my fault, possibly deliberate as part of the crossover. ("I meant to do that.")
DoctorV is providing art for each chapter; links are in my profile. Thanks to Sabrina06 and DoctorV for beta-reading.
Timeline: (P&F side) Late sophomore year of high school; Phineas, Ferb, and Isabella are all fifteen. (Narbonic/Skin Horse side) Some time after "If I Ran The Zoo" but before "The Terrible, Horrible, No Good, Very Bad Day". Note: this story contains spoilers for Narbonic's main story-line, and for Skin Horse through "If I Ran The Zoo". I've tried to make this understandable for people who have only read one side of the crossover, although it's probably more comprehensible for P&F fans than SH/N fans.
Isabella Garcia-Shapiro walked through the grey halls of Danville High School, pretending she couldn't hear the names whispered behind her back. "Freak." "Weirdo." "Psycho." "Crazy."
She sighed. Life had been so much easier when they were younger. Phineas and Ferb had invented cool things, and everyone had loved them. She'd led a strong troop of Fireside Girls that had gathered record numbers of the most obscure patches, largely with Phineas and Ferb's help.
And then, people grew up. They stopped enjoying the things that Phineas and Ferb had made. Some kids literally couldn't see the mutant potatoes running down the street, and everyone else pretended not to. One by one, their friends had drifted away, the stench of unpopularity chasing them off. It wasn't cool to do incredible things any more. The Fireside Girls troop had shed members until, finally, it had just been Isabella and Gretchen. And then Gretchen's mom had pulled her out because of the rumors that Isabella saw things that weren't real.
Phineas didn't seem to get upset about it. Isabella still had a massive crush on the boy, and he still didn't seem to realize it, but he really liked having her around. He was equally a target of derision, and Ferb even more so with his green hair. But the boys kept inventing; they just kept it to themselves, with only her for support. No more city-wide roller coasters; instead, they built invisibility screens and force shields to protect themselves - and her - from bullies. Unfortunately, she'd left her force shield at home today.
Isabella paused at the front door of the school, where a cluster of upperclassmen were gathered on the steps outside, chatting at the end of the day. Several of the cheerleaders were among them, including Karen, one of the leaders of their social circle. Unfortunately, Karen seemed unable to see anything unusual. One of the boys' last public inventions had been a giant robot for the homecoming parade, and when it had been suddenly destroyed, a falling piece had splashed Karen with mud. Karen hadn't noticed the robot or the falling machinery; all she'd seen was Isabella picking herself up, and she had decided that Isabella must have deliberately hit her with the mud. Karen had declared Isabella persona non grata after that, and had done whatever she could to make Isabella's time in school a living hell.
The teleporter in Isabella's pocket felt like it was going to burn a hole right through her jeans, and she could use it as soon as she got outside and away from people, but first…
There was nothing to be done about it. She had to get out, and as quickly as possible. Karen was laughing with her boyfriend, so maybe Isabella could get past without being noticed.
She slipped through the door in a cluster of other students, hoping to make it through the gauntlet unscathed. She was passing behind Karen, thinking she may have made it, when Karen suddenly stuck a foot backwards, tripping her. She tumbled down the stairs, miraculously not bringing anyone else down with her as her books went flying. She picked herself up, finding that she only had some minor scrapes and bruises, and hurriedly gathered her books as the cheerleaders and their boyfriends laughed at her.
She felt something within her snap, and unbidden, an idea for revenge jumped into her mind. She saw how to build it. It was simplicity itself, she just needed to gather the parts. And then she'd show Karen and the rest of her cronies that these things were real. She'd show them all.