Kao coins will stay isolated. Kao coins are very limited in scope - you get one per quiz, and cannot get them outside of the quizzing environment.
This is mainly a replacement (plus expansion) of the hanko system - which tracks activity across all of renshuu. So you'll be able to get the points to this system through just about everything you do here - I don't want to force people into specific ways of using renshuu.
My current idea is to have something like daily/weekly/longer achievements (that you can customize somewhat) that encourage good and varied study habits.
If anything, it will encroach somewhat on the daily challenges, but much more varied and extensive.
So (and this is just for the sake of the conversation), your daily achievements may be:
study 10 items (5 points)
do one quiz (2 points)
learn 2 new things (5 points)
play 1 game on renshuu (1 point)
get 5 questions correct (3 points)
weekly might be:
study 4 times this week
learn 20 new things
etc.
and then "permanent" ones would be not tied to any specific time period
learn xx words (first one is 10, next is 25, next is 50, 100, etc...just like the current achievements)
A bit later down the line, I want to let users "build" their own goals as well, as I often see on the discord that people have very personal goals that work for their lifestyle, limitations, etc.