I'm grinning ear to ear for this question cause the string tech and essence tech is one of my favorite bits in the BtM au! Also you don't have to apologise! Getting asks for my AU makes me so happy and are welcome!
So first thing is a bit of background lore for tech in this AU. Really important but uh basically all advanced tech has its origins in the Funk Tribe since in the movie they were portrayed to have a bit of sci-fi ish (this is just my interpretation btw) aesthetic and I decided to keep the same. In the context of the AU though, during the beginning of King Thrash's reign (he was a like a 16 at that point) he would succeed his mom's plan of waging war for unification since she died unexpectedly and as stated in chapter 6 in Tresillo's Pov. The Funk Tribe and Vibe city fell after Thrash's deadly attack and a good portion of the tribe came under control of rock.
The current string tech in the AU is based off the OG Funk tribe's tech or at least what was left of it in the wake of the fall. Since when the Funk tribe fell, Rock took a majority of their tech leaving only some of the stragglers and refugees who made their way to the Country Tribe and the Bounty Hunting World some bits and pieces of their tech. They ended creating the string tech though to combat Rock's growing power. At that point in time, they still had to figure out how to use funk tech cause like funk Tech could only run on Funk Essence so it didn't work. Anyways to explain the string tech more.
So how it works is that in this AU each string has their own unique power right? As I explained here before. But within the present Timeline of the Bergen Colony, Rock already has 3 strings (Techno, Classical and their own). In the resistance their mostly country and neutral trolls that make them up and some main tribe ones are sprinkled in between. But here's the thing, the 6 main tribes are the only ones that have special abilities cause like their the first 6. And for a long time only main tribe trolls like country, classical, etc could wield these powers and some trolls if they had some type of close ancestry so like if your half or at the very least quarter part.
There are two main types of techs, Copy String and Essence Fuse tech.
This is what I've talked about before where basically this type of tech can replicate the OG musical strings and mass produce power sources for stringed weapons. So like copy strings are fantasy ammo with cool ass powers that can be used. Like with Augusta (classical oc) though I haven't shown her in action yet, her main weapon is a Classical Copy String Rifle where basically blasts from it can yeah kill but also if she focuses her energy well enough she can actually shoot barriers to protect her allies. So like she would shoot on the ground near her ally and then suddenly a barrier like shield with come out to block an incoming attack. Of course other string weapons with other tribal copy string does different thing corresponding to their tribal music or something relating to their environment. Like Rock its destructive chordstrikes/soundwaves, Pop is attacking vegetation, Country is Land alteration (think earthbending but less control), and Techno is forced water pressure (thanks for @sorimisstuff suggesting way back last year)
You might be asking how are copy strings made if Techno and Classical's string aren't here to be replicated?
Simple. They don't need the OG string just the musical essence by this I mean main tribe trolls in and out of the resistance can donate (read mandatory) their musical essence to be created into copy strings. Btw the resistance does have land it has under control off, those lands being some parts of country given to them and some re-settled from Rock or some conflict from small hunting groups.
Also rock can make copy strings too since they literally took over classical lands and most of Techno, so lots of sources. And they have the literal OG strings, its just not that common due to a mix of pride and musical suppression with the whole "UNder oNE gENrE" thing they have going on.
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So when it comes to copy string tech the big downside for it is that copy strings specifically in the resistance don't last that long. Like copy string can be used up to about 2 hours at most. Rock doesn't have this problem with their own version of copy string tech since they have more resources to make it better while the resistance is still stuck with its old version.
And also, they can really only use string weapons with that corresponds with their own birth genre or subgenre. Augusta can only use classical strings while Nile can only use Techno. If either of them tries to use a different copy string weapon it wouldn't work cause their birth essence doesn't align.
But the other side with copy string tech is that it's easier on the body cause like the most copy string/ string weapons will do to a troll is really just use their own essence just as a stabiliser. Which is why trying to use string weapons that aren't your own genre type will not work. Along with that its separate and more controlled type of power.
Okay so this one is a new lore tidbit I got from your last asks that actually helped me make new plot point for later storylines so thanks for that :)
To explain, essence fused tech are like these small viles filled to the brim with the purest and powerful essence mixed with special boosting diamonds that trolls could take to basically go into super OP mode. Like an ultimate move you can pull off. Where basically a troll without a stringed weapon can wield two tribe's powers just by themselves. At the cost of your life, cause a troll's body biologically can't handle two simultaneous forms of powerful essence at once. Even trolls who say are like half funk and tech for example can't survive even when they were born half of both tribes. Cause the sheer amount of power that gets injected into the body will basically overwhelm them after a while and the body breaks down as it can't handle it anymore. This whole Essence Fuse is actually considered in universe as a last resort but of course there are cases where it wasn't like that but that's another thing entirely.
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As for what inspired me to use talent/musical essence as superpowers in my fanfiction?
Honestly the BtM AU started out as a crystal!JD AU where troll trafficking/ trollnapping was more common and JD along with the WT bounty hunters were like dysfunctional police squad trying to crack down on it for money. And well the crystal dory narrative would play out with the hunters and the brothers. In that OG outline I already had the headcanon with what TBT showed us that Trolls "talent" is their lifeforce. Then I ended thinking "But wait what if talent/life force could be like fuel for something other than giving rageons talent?"
Then it snowballed from there with me at that time making an outline for a canon-divergence WT AU where Rock won and there would like a resistance led by OCs and some brozone members. Then lightbulb I ended up merging those two wips into one and you got the BtM AU as it is now.
Though I can also say that some other shows that inspired me would be Attack on Titan, Code Geasse, and the Iron Widow book series since I was super into those shows when I started making my AU.
