Tsuruha Drug is a national Japanese chain that offers a huge range of cosmetics, toiletries and over the counter drugs. Tsuruha Drug has a store in Kutchan, and is one of the best places to purchase over the counter drugs if you're visiting the Niseko region.
Tsuruha Drug stocks one of the largest ranges of over the counter drugs and vitamins, and although the staff speak limited English, they are usually able to assist you by recommending the most common drugs for your symptoms. The store features English signage which can help you find most things, but if you're after something more specific, you may indeed need to ask staff to assist you.
There is an impressive range of beauty and sanitary products, along with the usual laundry and daily household cleaning products, most of which are cheaper and come in larger sizes compared to the products that the local supermarkets carry. One popular item I recommend are the Japanese bath tablets, which I've been told by locals provide similar nutrients to natural onsens and are very cheap at only 50 yen.
Be advised that Japan's over the counter drugs are often weaker compared to most western pharmaceuticals and falling ill while you're on holiday in Japan can become much more expensive compared to back home. Two years ago, whilst working in Hirafu, I caught the usual cold that was going around the village during the harsh winter. Usually when I have similar symptoms back home, a visit to the local chemist to get a single course of the necessary medications would only cost approximately $15.
I found that two courses were comparable to a single course of western medication and as a result, the cost of getting ill immediately doubles. I was also recommended some vitamin supplements on top of two courses of cold & flu medications and paid close to 4,000 yen, a relatively expensive exercise. This being said, I highly recommend you bring your own selection of drugs while on holiday in Japan to save yourself the frustration of getting ill.