Just returned from three nights on Rishiri (Feb3-5th, 2019), with two days of skiing backcountry. We tried to hire a guide months ahead of time, but it was a fiasco. We basically self-guided; rented cars in Sapporo, drove to Wakkanai, took the ferry to Rishiri. I wish more unbiased information existed about this place. This is a windswept island with frequent storms and closed roads. When the sun breaks, there is a sort of savage beauty to it; blue-green swells smashing icy shorelines, spindrift, blowing snow.

On the mountain, the snow is often windpacked, the snowpack highly variable. The snow itself was the consistency of wheat flower; squeaky, packed, slabby. Variable density layers as you dig down. Shallow snow in the windswept areas with exposed bamboo and low bent-over spruce brambles. Skiing was only OK relative to the rest of Hokkaido, but it is a neat place in the world to visit. Lots of lovely terrain, should the weather and snow hold for a number of days. You won't see many other people around the island, but you may see a lot of skiers if you're in a tour group.
See our video here