I have to give this story bible some massive praise. There isn't a single thing here that I don't like.
@Jon and the rest of the TTV cast, this is phenomenal work! I'm particularly fond of how well you've managed to make this world feel real, and in a way that isn't extremely complicated like G1. Alongside that, you've melded a lot of the great aspects of both generations into a coherent world! You all deserve tremendous praise, because working on this is no small feat.
Just some random bits I wanted to express:
I love how every region of Arthaka has a different form of society. The Mangai is brutish and gladiatorial like the Romans, Naho is like the Amazons of Greek legend, Tiro is the Greeks proper, Ihu is medieval serfdom, Motara is like the Wild West or Mad Max, and Kanae is..well, I can't draw a clear analog, but their culture is unique in terms of how its economic position affects the population.
I'm hoping to see a lot of the character development of the Toa focusing on how they can find their Unity, despite being of so vastly different societies, and maybe how that affects the relationships between their regions as well.
The way you've integrated the lore of G1 while also putting a fresh twist on it is wonderful! Your use of older characters is really exciting to me, especially Jaller and Velika, as well as the Elemental Gods.
Also, this was just a little nitpick inconsistency I've noticed, but the story bible clearly mentions that the people of Ihu are logic and reason-focused and disapprove of the religions of other regions, yet their main rivalry is with the people of Managai. I realize this is to parallel the traditional Tahu/Kopaka rivalry as well as the natural opposition between Fire and Ice, but if the Ihuans'(?) disapprove of the beliefs of the other regions, wouldn't their main rivalry then be with the religion-heavy Naho? Just something I noticed that doesn't need to be changed, but seems inconsistent anyway when those points are brought up so close together.
All in all, I'm very impressed with everything and very excited for the future! Good work and good luck!