Before I begin ye Post of Criticism, I should mention that I love the system's basic rules. Elegant, sensible, and occupying a pretty good spot between using precedent and incorporating novelty, so that you get the sense that it's new without having to strain yourself to compare it to what's come before.
Moving on to the less complimenty stuff,
which I'm gonna keep updating as I read through this:
Devil in the Details should probably have "spell" changed to "class feature".
Blindsight and See in Darkness are pretty redundant (blindsight is strictly better) as mutations, so you might consider lowering See in Darkness to a lower level, or lifting the range limitation. Similarly, darkvision is kind of a weak choice compared to the other initiate options, particularly since it's such a common racial trait.
Devour needs to specifically let you attack a creature you've pinned; the default grapple rules specify that you can't attack when you're pinning, only make a grapple check to deal damage as if by an unarmed strike (which a bite attack isn't). The original rules are silent on natural attacks specifically, but the Rules Compendium lists them alongside manufactured weapon attacks, when discussing your options in a grapple.
Explicit statements about stacking need to be made in rules that seem designed to allow you to spend tama for cumulative bonuses (a kagaribito's Pyros Reactor, for instance). Since same-typed bonuses don't stack, for instance, you could only ever get a +1 racial bonus out of it no matter how much tama you spent (for instance, spending 5 would leave you with 5 separate +1 bonuses, as worded currently).
Also, in related news, kagaribitos are kind of crazy-awesome; a racial trait that scales that well with level is really good, particularly with a lingering duration instead of a one-time-event sort of thing (one attack roll, one save, etc). The best analogue is probably an elan. Aberration vs living construct is probably a wash in terms of awesome types, but I think a kagaribito has access to more powerful abilities, and doesn't have net negative ability scores. You might add another ability score penalty to balance this out (note that the standard living construct, the Warforged, also has a net negative).
EDIT: Read through the stuff that isn't techniques or feats, which I'll probably look at in more detail if and when I build an akashic character.