Niseko is generally very safe for solo female travelers. The local people are extremely friendly and respectful. The crime rate is very low, and people are typically willing to help if you run into any trouble. There's a very low chance of getting into unsafe situations as long as common sense precautions are followed. Public transportation and taxi services are safe to use. As with anywhere, it's crucial to stay aware of your surroundings, especially at night, although Niseko is typically safe even then.