Quite a fun story! The Tahtorak howdah is a great idea, and I love the simple eloquence of the “painstaff.” It’s one of those things where the name gives you all the context you need. And as a 2006 fan, I appreciate the callback to “deformed Matoran.”
I also love how you’ve imagined the Av-Matoran in their original homeland. It’s a lot more flavorful than how I’ve always pictured it (ie, just boring caves). There’s real life to this world you’ve created for them, and I’d love to see more of it in some capacity.
If we’re talking about canon, I’m not sure I 100% buy the conceit of the Barraki discovering where the Av-Matoran are in the first place, and then subsequently them being able to keep it a secret. That feels like a big enough thing that it’d probably come up somewhere, somehow. But on the other hand you’ve given Pridak, Mantax, and the rest of the Barraki enough of a reason to keep them a closely-guarded secret, and I can believe that if this did happen, then enough time would have passed that the location of the Av-Matoran would’ve passed into legend and then forgotten by the modern day of 2008’s storyline.
And speaking of the Barraki, I really enjoy the pairing of Pridak and Mantax. As far as I recall, that’s not a combo we ever saw represented in the official storyline, so seeing how they interact and react to each other was a real pleasure to read. Pridak’s calculating nature is quite interesting to see here, and him always being on constant edge, assessing how he stands compared to those around him, is something that makes sense for him, feeding into his pride and ego. The Governor’s a fun character too, with her reaction to them arriving a good bit of characterization, particularly how she compares her faux scars to Pridak’s real ones.
All in all, lots of good stuff here!