From MangaHelpers:

The normal world has become connected to a magical world. Now there is a castle nearby, with a gate that sometimes allows mischievous fairies to pass through into the usual human world to cause trouble. Guided by a magic cat, Akari and Kano have become "magical sisters," who transform to battle the fairies and force them back into their own world. Akari and Kano mess up a lot, but they're doing the best they can to be good protectors! [tethysdust]