how long does it take to lvl up to 100 (or 99) in re: com with sora(my lvl is 67) and riku (lvl 56) and also how long does it take to finish 100% in the whole game?

Well it depends.

If you're using a powerfull deck with Sora, it's best if you go to Castle Oblivion and defeat as many Heartless as you can (trust me, it works), so it will take a while (around 4/5 days, if you play all the time it'll take less time).

About Riku his deck varies, the deck changes if you go to other worlds. Again go to Castle Oblivion and defeat as many Heartless as you can (same time as Sora, goes faster if you transform into Dark Riku).

If you want a tip on how you earn exp faster, then go to Destiny Isalnds and use Mega Flare which will destroy every heartless in the area and takes 3-4 seconds to win a battle.

If you want a tip on how you earn exp faster, then go to Destiny Isalnds and use Mega Flare which will destroy every heartless in the area and takes 3-4 seconds to win a battle.

 

Exactly just use mega flare

Well, leveling up has seemed like a pretty grueling process for me. But getting 100% can be quick and it can be slow, it all just depends on how quickly you manage to get enemy cards from Heartless. Generally the Heartless drop cards randomly, I would assume that there are some ways of killing a Heartless that improve the chances of them dropping their enemy card, like killing a Blue Rhapsody with a Fire based attack. Of course, you do have to kill an enemy last if you expect to get their enemy card, but I'm sure you know that.

 

And the tip on this thread about using Mega Flare on Destiny Islands is a good one, even though I've never tried it. Now you might be thinking, well why can't I do it on the 13th floor. If you don't realize why, it, my guess being, has to do with the fact that there are enemies that can absorb certain magic, and I'd assume that Mega Flare would be categorized as a Fire based attack. Also, there are the annoying Neo Shadows that might go in the ground before you can use it which would suck.