I'm wondering, how does the in-game rank system work? oO

its based on how many matches you have played compared to others of your same belt

Its based on your qi(within belt ranges) and win ratio. So to have a good rank you have to win most of your games.

What Fish said. Basically the higher up you are in your belt. Lets say you are 10 games away from your next belt, that would mean that you are going to be like rank 1-20 considering on your win/lose ratio.

Example.

I'm a 10th Dan Black Belt.
My Rank is 82.
This means out of all the 10th Dan Black belts, I rank 82nd in comparison to my Qi and win ration.