Alright, I was gonna do Tenzin next, but I'm gonna do asami instead. Partially because I want to get the main cast out of the way and partially because these things are getting too damn long.
So...Asami. You see, the issue with her is that she actually isn't that bad. I still praise her as the only competently written person in Season 1. It's hard to know what to change with her, but she can't function the same as she did before. At the same time, I want to keep her integral involvement similar, but...more, I guess.
But before that, I want to paint a small picture of her life. If her mother had died when she was young, she'd be left without a mother figure, but also few memories. Her mothers absence in her life growing up would be more felt than her separation from her. So rather than six, I'm moving the age up to 14. Her mother isn't some stranger in photographs and vague memories. She knew her, and she had a large impact on her. Yasuko was race car driver. In fact, she was one of the first ever, as cars were a relatively new phenomenon. She actually didn't have much of an education and mostly tended to her family's resturant, but once she found out that she wanted to drive, she put all her effort into it. She learned mechanics through reading books Republic City Library and worked to save up enough movie to get her own car. It was kind of a piece of trash, but her studies paid off in allowing her to modify it into something more decent than anything it should have been. She was a rare middle class person to own one, as they were still very new, so when she actually brought it to race, she was a true surprise hit against cars that were sponsored by actual companies. And since she had the good sense to bet on herself in a competition where she was expected to place last, she made her fortune in a 18.5 seconds over a quarter mile.
You would think that this would be where she had met Hiroshi, but it would actually be on a lazy afternoon some years late, when his car would be break down in front of her shop. She would be working on her car in the garage, as he walked up. He'd ask for assistance, which of course she'd give. He noticed her she was stripping out the engine and was tinkering with this and meddling with that. "What are you doing?", he asked, incrediously. He told her she ought to use so and so, and she explained why he was wrong (I don't know mechanical engineering, so imagine some fancy terms), and she told him he had no idea what he was talking about. He introduced himself in a huff, head of Future Industies, which made her introduce herself, as a renowned racer. They finally made it into a bet, which they resolved fairly quickly in her favor, and he had to work as a cook in her resturant, where he reclaimed some dignity by being the best cook she ever had, and they became much more friendly and intrigued by each other since then. She never was officially a part of Future industries until they got married as she didn't see the point in working under him, but she had been his partner in all but name, having input on the Future Industry cars that would be a roaring success.
Asami loves her father dearly, but it's clear who she took after, and when Asami always imagined that when her prince charming shows up, it will be like that. Now, when you get a child obsessed with something or another, they learn it very fast, and if you nurture that, you get what is often called a genius. Asami will always love driving and her fondest memories are those driving with her mother, her teaching her how to take apart a car and understanding how to make it better, but she didn't breathe it as Yasuko did, so while she learned a lot, she didn't feel crazy about it. What she did leave her, however, was knowledge on how to obsess over something. She learned how to place herself so deeply into the study of a thing that she couldn't leave until she mastered it. So when decided to play an instrument or do theatre or design fashion, she did it with a fire that burned until she mastered the thing. And once it was done, she'd put it away, placing it on a metaphoric shelf, collecting skills like trophies.
So...she heard her mother killed by a firebender at 14. She was taking out trash from her family resturant, which she visited to help her parents a bit. She was with Hiroshi when she died. You can imagine what kind of impression it made. And what kind of fire it sparked within her then. She had already been training in martial arts. She learned non-bender forms a derivative of firebending and Chi-blocking. But now she had a mission. She would find her mothers killer. She knew he was part of the Triple Triad. From there...
Well, I'm gonna be honest and blatantly steal a concept idea from another fanfic because it is WAY too fucking awesome not to use. The Night Shade. It's a dead fic anyway, but it's got a word count of 50,000 if you're interested, and it's alternative title is Batsami begins. I haven't read it, so I can't vouch, but she's basically a masked superhero. And Asami works the same angle here, at first. At 14 though, even as skilled as she is, she fails. She doesn't know where to start and she isn't as skilled as she needs to be. But at the same time, the trail gets colder the longer she waits. So she goes out, in disguise, trying to find them. She manages to find one and tail him. She doesn't get far, she gets caught. She has to fight her way out. She gets beat up a lot, but she eventually wins. She demands that the guy tell her, but he doesn't know. So she beats him harder, and demands the secret. He still doesn't know. So harder. Still doesn't know. At the end, she's just crying as the guy is knocked out beside her, unable to do anything. A larger group of triads spots her, and she has no choice but to run, less because they might kill her and more because she can't handle this failure.
It wasn't a night she liked to think on but she didn't give up. She met failure many times before. Jumping into a situation and trying to punch the answer out of a guy wasn't going to work (which would explain her frustration with a certain someone later on), so she fanned out. She began to develop connections with the underground from a higher place of social status. She learned what was going on. More than anything, she threw herself into training. She mastered chiblocking, and made sure to learn the nonbending variations of earth, water and fire bending as well. Those weren't nearly as effective offensively, but it did wonders for being able to defend against them. She brought her knowledge of engineering to her purpose and developed the electric glove without anyone knowing. And at 15, she took on the Blue Spirit mask, a known savior spirit that aided the avatar on many adventures (legends have kind of spun out of control of Aang's TLA journey and future adventures), ruining Triad operations wherever she could. At some point, she didn't know when, it wasn't enough that she find her mothers killer. He, she concluded, probably had reasons for doing what he did. She learned things about the triple triad as she spent time studying them, taking them apart. She had expected to hate them all, but she found cases where the benders clearly had no choice. For a long time, she struggled with guilt, thinking she should hate them all, just on principle. But it was the Triad, as a system, that made this and other horrors. One day, she didn't know when, she just realized the obvious truth: The Triad itself had to be destroyed.
Which she couldn't manage. She could disrupt individual operations, but there were always dozens going on at once, and the leaders were well protected. She can't really go to the police about it, as Lin wouldn't accept ill gotten information, so none of her interrogations were ever useful in that regard. For a long time, she thought Lin was corrupt just for how incorruptible she seemed, but later realized she was just that true regarding her oath. The two worked with each other in grudging tandem when circumstances allowed. But ultimately, they were always one step ahead, every single time. It was like hitting water. Any disturbance they caused would settle and reform.
Enter Korra. She knew Korra would make a difference she could never make on her own the moment she destroyed that Triad warehouse with Mako. She needed to meet her. She wasn't normally manipulative and was confident in her personal friendliness and charm, but she had to have Korra at her side. She would be invaluable. She had no idea how though. She'd need to think on it, so she'd go to her gym and come up with a plan. And she did that, practicing her fire-nonbending. Until she heard Korra's voice, someone incredulous at seeing a nonbender practice firebending, say behind her, "What you doing?"
Asami would have the most plot relevant involvement, as before. She'd discover her father to be after firebenders, and be emotionally torn over that. If you're wondering why her father seemingly doesn't notice his daughter going out at night to crusade, it's because he's in a dark place, plotting away his revenge with the Equalist movement. Yasuko's death has split them apart, something she realizes only later. But her goal is to remove the Triad. It's a complete perversion of what she believes that Republic City should stand for, and she wants justice for her mother. The mystery of who killed her still drives her, though at this point she knows it will almost be impossible to find out who did it. It's a crime 2 years old. The gang member himself might already be dead. But still, she can't not do this. It's her greatest goal.
As far as her romance goes, she'd actually be interested in Mako, but that'd be mostly lowkey and Korra would give precisely no shit about it. Mako's not good enough to be her bae, as he is. But to Asami, Mako would basically be the picture perfect guy who the Triad had crushed and lucky enough to escape. In a way, this attracts her more to him than Bolin, who remained largely safe from it because of his sacrificial efforts. In a way, Mako is representative of why she can't just hate the entire Triad group. They preyed on the weak and vulnerable, and their shared experience of death of parents creates a particular bond with them.
As far as Korra goes, I know she's coming off a bit manipulative here (or would be if she had the chance to make the introductions she wanted to), but by the time I got her backstory and current activities down, it was difficult to think of how else she could react to seeing the Goddamn avatar trash a triad warehouse besides "I NEED YOU ON MY TEAM" In a way, Asami views Korra most realistically, seeing her as the hero she is meant to be, and her activities allow her to empathize with her stuggles to an extent. Unlike the brothers, both girls come from priveledge, though they are two very different kinds. And while a romance will bloom in them eventually, Asami is currently in the part of her life were she thinks she likes just boys, so she doesn't really notice her romantically. Korra, in turn, just kind of sees her....not sexually, but thinks "Damn, she's attractive" without realizing that she is specifically attracted to her rather than just noticing an attractive specimen of her gender. Ah, the awkward mysteries of teenage years.
Lastly, with Tenzin. I stopped at the meeting with Korra, but she joins Korra as an apprentice to airbending, her practicing a nonbending variant on it. They would also develop a mentor relationship, with Tenzin being her emotional mentor compared to Korra's spiritual one.
That's all I got written for Asami so far, but I have more in my head, and with this, we're starting to touch the edges of the main plot.