Tateyama is generally very secure for solo female travelers. It's one of the renowned tourist spots in Japan and is known for its low crime rate. Locals are respectful and helpful more often than not. Plus, Japan as a country prides itself on its safety and cleanliness. The public transportation is also reliable and secure, even during the night. However, just like in any other place worldwide, it's always advisable to take normal precautions such as not walking alone late at night in less crowded areas and keeping your belongings secure.