Uayward Son

Question: In your system, does the Maya idea of uay work similarly to how you worked the nagual?

Question: Love the nahualli of the Aztec, what about the wayob of the Maya?

Yes, as a matter of fact! While we don't have any active K'uh running around right now, we would be inclined to use a similar model for uayob as we do for nahualli, setting them up as customized special Birthrights tailored to the Scion who is attached to them. The concepts are similar enough that most of the nahualli Birthright effects make sense for a Maya Scion as well, so those who want to use the same template can go right on trucking.

There are some differences between the Aztec idea of the nahualli and the Maya idea of the uay, however, which may require that Storytellers and players investigate alternatives and get creative. Where nahualli are always animals with no exceptions, uayob are usually animals but can appear in other forms as well, such as the famous skeleton uayob of the Underworld deities. There's also an interesting concept among the Maya that doesn't appear for the Aztecs of animals having uay of their own, so where a Scion might have an animal as a uay, an animal might have a human twin, or another animal, that behaves similarly for it. You might be able to do some particularly neat things with a Scion who has a Birthright Creature and is its uay, providing it unusual bonuses or abilities (but remember to keep this all reasonably Birthright cost-appropriate!). Finally, the Aztec concept of a nahualli hits the idea of the other half of the soul very hard, but the Maya concept of the uay, while incorporating the same idea, tends more toward illustrating a figure's magical powers, so you may want to experiment with uayob being less about the Scion's personal attributes and self and more about things he can do.

Uayob aren't up to the totally crazy level of inclusion as, say, the Deva vahanas which can basically be any darn thing in the world; for most PCs, they'll probably be animals and the nahualli template will work perfectly well for them. But if you have a player who's really interested in the subject and willing to do some research to come up with a cool new idea, by all means, tinker away until it fits.