Okay, okay, okay, so I know this has been done a million times by now, but I wanted to tackle the idea from my own personal narrative perspective. So, here we go –
Shiro – Gifted earthbender that was raised inside Ba Sing Se and was being trained as a member of the Dai Li before he was abducted by firebenders and taken prisoner. His abduction was a result of a plan by the Fire Nation to secretly infiltrate the Earth Kingdom and take down its most gifted benders. Before he was realized as being talented and brought in to train for the Dai Li, he lived in the lower ring of the city with Keith, who’d he’d long since adopted as a younger brother. They found out during their youth, however, that Keith was a firebender, which Shiro told Keith had to be kept secret. He encouraged Keith to learn his talents nonetheless, if only for self-defense. After he’s kidnapped, he loses his arm and his tortured, etc, and eventually develops metalbending out of sheer desperation to escape. Metalbending is what allowed him to create and use a metal arm as replacement for the one he lost. He eventually gets away—after learning that the Dai Li has been corrupted and secretly overtaken by firebenders—and goes back to the city to find Keith. But when he returns to Ba Sing Se, he comes home to find that Keith is gone and clearly has been for some time.
Keith – Firebender. A very good firebender, in fact, but too ashamed of his talents to really do much with them. He grew up with Shiro in the lower ring of Ba Sing Se—basically poor—and grows so distressed when Shiro disappears that he lashes out at the Ba Sing Se law enforcers. His status as a firebender is revealed and he has no choice but to flee the city. He’d planned on leaving anyway to go looking for Shiro, and so it becomes his mission to find his older brother—even if he has to search the entire world. Unbeknownst to Keith, however, he was tossed out of the Fire Nation palace as a baby because he was an unwanted bastard son to the Fire Lord. Also, spoilers, he’s the Avatar as well, but is unaware of the fact due to how subdued he’s been forced to keep his talents his whole life. Lots of drama for Keith, haha. Poor child just wants his brother back. Oh well.
Lance – Waterbender from the Northern Water Tribe. Prince, though he’s nowhere near being in line to become chief. Still, there are plenty of responsibilities he has, but he decides to run away in search of adventure instead, wanting—more than anything—to be a hero and stand out, basically. He’s had this plan since he was a child—was his dream to see the world—and so he spent a lot of time not only mastering waterbending, but the spiritual connection and teachings of the Northern Water Tribe, as well as healing despite the fact that, as a male, he wouldn’t normally know how to heal. Though he wasn’t the most gifted waterbender, he spent most of his youth studying and practicing in preparation for his big leap out into the world. As a result of being a healer and having studied the spirits extensively, he’s very knowledgeable, but generally keeps these things to himself (wants to be a lady’s man, not a nerd, basically). He is a bit spoiled nonetheless, and doesn’t have a real realistic idea of what’s going on in the world. He and Keith are both opposites and foils as a result of their upbringing and positions.
Pidge – Waterbender from the Foggy Swamp Tribe. Her father was an inventor from the Earth Kingdom, however, who found himself studying the energy levels of the swamp area before meeting her mother and promptly falling in love. Her brother and father are earthbenders, while she and her mother are waterbenders. And while she is trained in the techniques of swamp people waterbending, Pidge is far more interested in technology and the things her father studies. Her father and brother make regular trips into the earth kingdom—for research supplies, etc—and eventually end up abducted by the Fire Nation for being meddlers or something. Which inspires Pidge to leave her home in search of them, determined to rescue them much like Keith is aiming to rescue Shiro. She isn’t one to be trifled with, however. While she doesn’t have much interest in bending, she is trained and is more than capable of defending herself, as well as using the plants around her to her advantage. She and Lance practice very different types of waterbending as a result, but this doesn’t come between them or anything. They probably bond over it, actually.
Hunk – Earthbender. He’s from a small village to the north that is occupied by the Fire Nation and generally has no interest in getting involved with business outside of it. However, when Lance shows up and causes a ruckus (no doubt by accident), he gets caught up in it and ends up wanted by the fire nation and unable to return home because, if he did, he’d be putting his family in danger (they’re already in danger from the Fire Nation, but Hunk is kind of sheltered and naïve). So he ends up tagging along with Lance, deciding that he’d simply go to the Fire Nation higher ups and explain the misunderstanding, thus clearing his name and allowing him to go home. Obviously, he learns that this isn’t really going to work and that the conflict is much larger than he and Lance really realized. Upon seeing how people are suffering because of the Fire Nation, Hunk vows to do all he can to stop it.
Allura and Coran – The last two airbenders in the world. They were originally part of a secret society that—after the airbenders were basically destroyed—vowed to find the new avatar (who was murdered during the airbender raids) and return balance to the world. However, the society has basically died out and so Allura and Coran are all that’s left. They’re still going around the world, searching, but to say the mission has kind of become hopeless is a bit of an understatement. Still, they’re determined, convinced that if they can find the Avatar, they can stop the Fire Nation.
And so we have our misfit team of heroes whose paths eventually cross. Lance and Hunk come together first, and then probably end up with Pidge as a result of trying to help her (likely when she doesn’t need help), before those three maybe meet Keith in a prison where he’s searching for Shiro (they’re there because Pidge is looking for her family in the same place). Meanwhile, Shiro is hunting for Keith, knowing more about him than he realizes (Shiro knows Keith is the avatar, which is half the reason he was so protective over him. He probably saw him accidentally bend earth or something, but then lied and said he’d done it instead). He meets up with Allura and Coran, and as they have a shared interest in finding the avatar, they team up. Likely the two teams meet up as the finale of season 1 or something, where it’s revealed during a dramatic battle or something that Keith is the avatar before they all make a break for it.
Hunk and Shiro end up as Keith’s earthbending teachers, Allura is his airbending teacher, and Lance is his waterbending teacher (though neither are happy about it. Pidge doesn’t really have the knowledge to teach waterbending, or so she claims, though she does end up teaching Keith a thing or two as well). Water ends up being the element Keith has the most trouble with, which of course spurs antagonism between him and Lance. And when it’s revealed that Keith is actually a bastard prince from the fire nation, this makes things between him and Allura rather tense as well. While all this is happening, Lotor is around causing trouble like Azula did and we’re getting a more in-depth look at what Fire Lord Zarkon is really aiming to do. Basically he not only wants to take over the world, but the spirit world as well (which Haggar, his right hand lady and spiritual expert, thinks is silly—he should be content with the normal world, obv). Zarkon is looking for the avatar not to kill them, but to somehow remove the spirit of Raava and merge with it himself. This is becoming increasingly more difficult for him to do, however—especially with Keith getting stronger—and so he learns instead (maybe from the owl library that he forced his way into) about Vaatu being imprisoned and decides to instead merge with that spirit. Which is kind of what brings us to the season 2 finale. Probably the main group has split up because they’re fighting and they all get reunited in the end, where Keith tries to fight Zarkon and fails. And it’s Lance, who maybe shows up last, that uses his knowledge of spirits (which has basically been lost to Allura and Coran, despite them being airbenders) to separate Vaatu from Zarkon before a dark avatar can really be created. But as a result, he, Lance, ends up attached to Vaatu. Why? Because he and Keith were painted as foils for a reason, that’s why.
So basically Lance is all sorts of fucked up now, and is dealing with some pretty dark shit that Keith has to help him with, which kind of allows a friendship to form between them where there previously hadn’t been one. Through a lot of interaction and development between all the characters, they eventually come to understand that Vaatu being attached to a human is similar to having him imprisoned and that, so long as Lance remains uncorrupted, he should be able to function as a second avatar. After all, it’s about balance in the end, dark and light, yin and yang, and so while Keith and Lance seemingly oppose each other, they also complement each other. Thus Lance is the first Dark Avatar, a new avatar that will be reborn along with the original and will need to be trained in how to master the evil inside them or something like that. He gets to learn all the elements too, but probably isn’t a master by the time we reach the end of season 3, unlike Keith. Meanwhile, Zarkon is pissed and is like, fine, I don’t get an avatar spirit, I’ll create my own and he basically uses secrets taught to him by Haggar to harness raw spirit power for his own gain. Now he’s really dangerous and threatens all the worlds with potential destruction. And yeah, all of team avatar(s) have to work together to stop him!
I can’t decide if I should do a more in-depth outline for this or not. Like, one that reflects the importance of all the other characters, not just Lance and Keith, haha! Because, obv, they’re all crucial. I mean, clearly Shiro needs to have a personal connection to Zarkon, maybe even some kind of connection to the spirit world. And, like, I was thinking of trying to incorporate the lions as spirits of some kind too. I dunno–we’ll see XD