how to grind diamond characters
in fact, there is no fast way to get diamond fighters in the game, except for the diamond shard system
but i will say from experience, at low levels, diamond fighters are not needed. you will have plenty of good bronze and silver characters. also, at least, you have the opportunity to pump up at least one gold character by collecting resources in the story mode
it is true that diamonds are mostly better, but at low stages they will not be any different from all the other fighters of one rarity or another
in addition, you will clearly not have enough resources to pump up a diamond fighter, so allocate them to good characters, but with a lower rarity (again, bronze, silver and gold)
do not rush your game path, in the future you yourself will find ways to get diamond fighters
I don't really know how to grind theonite or canopy coins that well
kenopy is much easier to get, almost every mode (story mode, prize fights, parallel realms, etc) will reward you with this resource, just try to play more often in one mode or another and kenopy will almost always be with you
as for theonite, it is a little more difficult, since main way to get them (especially for a beginner) is the same story mode or prize fights