The Formative Years
Jo's parents were born in the United States, but moved to Japan for entrepernurial reasons. While heroes were not their main focus, Jo grew up an overachiever both due to and despite her parents' expectations. As an autistic child she got a lot of support but few social relations. The support she received was mainly for enabling her to work on academic pursuits, but she also maintained an interest in Pro Hero mainly becuase the profession was known to be difficult and the pinnacle of achievement for people born with powerful quirks.
Jo's quirk was never "powerful", but she acclimated to using it for daily activities fairly quickly, developing a dexterity with her braids despite the traditional laws regarding quirk usage that most people didn't bother with anyway aside from condemning villains. Sure, it was technically illegal for her to use her quirk freely, but plenty of people with quirks that made life more convenient such as simple telekinesis or similar things used theirs regularly and Jo saw this as a nonissue. However, due to a few scares involving overstimulation on a mental or sensory level, and others' reactions to such, Jo found herself wanting to be able to use her quirk/chomping at the bit a little, since such limitations bothered her.
Ultimately, given she was interested in being an overachiever anyway, the hero profession seemed like a way to grant her more freedom to use her quirk while also giving it- and her- a purpose. Having latched onto the concept in middle school, Jo focused her efforts on maintaining good grades, avoiding meltdowns, and micromanaging her life with a slim margin of error that would allow her to function at her best. While she cultivated a few friendships and was a bit of an oddball at times, eventually most of her relationships fell by the wayside once she reached the point of applying for hero school- of course, the very best, the most prestigious, U.A.
She figured that that was the first step towards making a life for herself where she would be able to play the role that would suit her best- that is, one she would build that would play to her strengths and that she would be able to maintian through adulthood and beyond.
Building a Purpose
Her high academic grades already carried her pretty far towards her goal, and the practical entrance exam was fairly straightforward, though she would never admit how she had nearly shattered under the pressure before dissociating in a way and burying her fear under the motivation to Get It Done. This itself became an important skill of sorts: separating the emotions from the awareness of necessity, and managing to prioritize action without being held back by fear. However, this was not a foolproof ability and ultimately was only a stopgap measure to deal with stress.
Considering that, she did still manage to get through the entrance exam and manage the curriculum of the school itself and her training. While it bothered her somewhat at times that she was putting herself behind a mask, she figured it was necessary and a valuable tool for self-improvement and striving toward her goal. Another way to go beyond her limitations- Plus Ultra and all that.
Her overall performance at U.A.'s hero course was regarded as good, decent, that she was capable of getting done what she needed to do, if a little rigid in her focus and methodology. She wanted to do better and prove that she could do better. So she trained extra hard and after graduation applied for Endeavor's Agency.
You have to push yourself past your fear, to go Plus Ultra and all that. I overcame my fear and kept pushing.
Again, her high marks in the academic and theoretical side of things got her further than somene else might, and even though many considered her quirk unsuited for this particular workplace, she managed to become a sidekick at the agency, mostly focusing on rescue and civilian management since she seemed to have a level head and a brave heart. She didn't often go head-to-head with villains, but she could break apart rubble with whacks from the metal spiked balls she would carry in her braids, climb walls to some extent with similar equipment, and direct civilians to evacuate or even grab them out of danger if needed with her braids.
She didn't see much of Endeavor directly, and often only watched from a distance as he took out threats and such. She didn't entirely mind being in the background, taking pride in her collateral damage record and making sure to do the best to complete her assignments- however, she did somewhat crave attention and took well to the praise of those she helped. She wanted to be seen as a rising star and hoped to become as well known as Endeavor one day, but she had her place and was willing to see it as a stepping stone for the moment.
She had a slight fear of stagnating, but she used that as motivation to get better at what she was good at.
Ambition is complicated when you reach your adult years, and knowing I'm still so far behind Endeavor has me chafing at the bit a little.
The Feud
It started out simple. Then things got complicated.
I'm dealing with it.
When the hero called Spiral first encountered the villain Dabi, it was in a situation where there was a lot of chaos during a LoV attack, and he managed to corner her, expecting her to freak out and beg for her life or something like the lesser heroes or civilians or even small-time wannabe villains he's killed.
But instead of caving into fear, Jo allowed herself to dissociate a bit knowing that this was a fight for survival and emotions would just get in the way.
Her facade of not being worried about the flames she was being threatened with pissed Dabi off, but by the time he realized she was acting in a way he didn't expect, she had cleared half the distance between them and nearly reached him with her braids, and he had to react defensively… which also pissed him off. Unfortunately for him, more heroes had arrived by that point and it was safer to retreat… he figured he could just track her down and burn her later, she was a hero so there would likely be a record of her identity, or at least the agency she worked for, somewhere.
Imagine how pissed he was finding out that she worked for Endeavor.
The Obsession
Dabi found himself looking into everything about her, and of course information about nearly anyone's identity can be found with the right price, or persuasion, with some notable exceptions of course. Everything he found, though, seemed to indicate at first that she had gotten lucky, that her admission to Endeavor's agency was a fluke of privilege, if anything. Because surely, with a weak quirk like hers, she wouldn't be suited to fight alongside the likes of Enji Todoroki. She clearly wasn't worthy, another false hero trying to ride on Endeavor's coattails.
He thinks- he thinks he can just play with me, the asshole!
But the more he read about her, the more he saw a pattern of sheer determination, a motivation to take whatever is thrown at her and overcome it, and that pissed him off even more.
He started wanting to break her.
When he started realizing he was seeing glimpses of her in every other passing stranger with even the slightest similarity of appearance, and getting constantly on edge because of it, he at first was in denial that any hero could have that affect on him.
Any hero other than Endeavor, of course. Though he was in denial over that, too.