When people dream, they express their utmost desires and emotions within the confines of their mind; but when their strong emotions cross the border into reality, the dream can turn into an uncontrollable nightmare. 
Touko and Rinko are sisters known as "yume tsukai" (dream users), and their job is to take care of these nightmares. Using toys as weapons, the girls must both destroy the nightmare and return the dream to its rightful owner before the nightmare does any sort of serious damage. 
Have no fear, Touko and Rinko are here! 
(Source: Anime-Planet)