So, i'm doing adult quest, it seems to be that i did all the prequests because i can enter karin tower.But i can't get quest from karin.

this is why you didn't get the quest from karin:
Step 1: Once you reach level 30, find and destroy the crate pictured below that you'll found at various locations in the Karin Forest zone. If a create isn't at one of the locations it's because someone probably destroyed it recently. You'll either need to wait until the crate re-spawns, change to a different channel, or try and find one at a different location.

You can do this step and the next one before you reach level 30, but you'll have to wait until level 30 to continue the quest line.

(copy from the guide http://www.dbocom.com/forum/showthread.php?t=6339) do the ticket quest and after go again to karin ;)