The car rental process was very simple, but the counter staff didn't know which insurance I had purchased, even though there was a rental details printed in Japanese. They still said they didn't know 😅. They also strongly recommended purchasing snow tires if you're going to areas prone to snow. The Japanese government has regulations requiring snow tires for certain areas during specific months. If the option isn't available, ask customer service to contact the rental company. Otherwise, if they don't have snow tires on site and you need them later, the rental company seems to have the right to refuse to rent to you, as insurance might not cover accidents. Luckily, it snowed on the day I rented the car! Also, definitely purchase an ETC (Electronic Toll Collection) device; it's very convenient.