Ok... I've not done this in a while- Nashtuku is in transition. I wasn't happy with what I had once I went back and looked at it, so I'm changing it. I'm going to try to update here a bit more often, and we'll start with updates about what I've done so far.

The first thing I've added.is a vowel harmony system. There are 5 vowels in Nashtuku, a, e, i, o, and u, both long and short variations.  There are two overlapping systems going on, there's a front/back harmony system, which involves i, e (front) and o, u (back). There is also a height harmony system involving only a (low) and e (high). a is transparent to the front harmony system, and i, o, and u are transparent to the height system. The controlling vowel is the first vowel in the word (noun or verb) Here's some examples:

bëri to talk

hada to understand, to know why, to understand the reason something happened

koti to go towards something

gumu to be in emotional pain

tsïlu to fall from the sky

I'll use some stripped down examples, using just an aspect marker 'e, which is the perfect marker

'ebëri nothing fun here...
'etsïlu this is the same, nothing fun, the 'e is front, and is not effected

'ahada  'e->'a for the height harmony

'ukoti 'e->'u for front harmony
'ugumu front harmony again

That's all for tonight, I've got a bunch more I've been working on, I'll try and update tomorrow...