Chims are black creatures (or other colors depending on the variety, really) that scuttle out of holes, hop off of small trolleys, fall out of trees or tall mushrooms, or something similar depending on the landscape. Kicking them provides you with Chimspheres, which are vital for completing some areas because of the Chim Doors.
To satisfy this, you only have to hit 30 or more. I do believe it counts if your party members kick them as well, meaning if you stand near a small trolley in a cave or feudal palace setting, you could have them clear them out for you by pressing the steam button 10 times. It's easier than trying to use your bike.