Rusutsu Resort is world famous for its deep powder and tree skiing. There are many areas in the resort where you may safely ski/board outside of the marked runs, these areas shown by the yellow areas on the map.
It is however important to pay attention to the out of bounds markers. The blue areas on the map are strictly out of bounds. There is no way back to the resort from these areas and it is necessary to be evacuated by ski patrol. There is a minimum of 50,000¥ fine for this.