Love the premise of the system! I didn't get to play it yet but here is some feedback from reading it:
I read it in ReadEra on Android and in the dark mode the white background of some pictures overlapped the text and made it unreadable. The two pictures on page 12 work as intended, so do whatever you did to those to the rest as well and that shouldn't be a problem.
You might want to rethink using the term water bender, as it feels dangerously close to copyright issues.
As for the actual content : I would allow to reroll 1s as a result from the Death table the first time they die and allow players to chose it freely instead. This way people that like high lethality will have it while keeping the rest of the group alive more likely.
I love how open the fluff text for Blessed of Water or Cleric of Small Gods is, I wish it was as open for other Callings (for example artificer or alchemist). Also it would be nice if they were organized alphabetically.
The cipher part of the Archivist's expert reader trivializes riddles, which I would dislike both as player and GM.
The Grimblade reads as if it is insanely strong (as said before, haven't played it yet). Combining from character creation on armor, a strong attack and the ability to cast spells. And the advanced abilities feel strong enough so that a Grimblade won't fall off later in the game.
I would have liked some examples, not necessary an exhaustive list, for the Cleric of Small Gods domains.
There are so many things I liked, from the artwork, to how things are written to mechanical implications, that pointing all of that out would be excruciatingly long. In conclusion: I love this and hope to see a finished version of this!