When I was planning my trip to Japan, I was sure the most important things were the routes and trains, and I only thought about internet at the last minute. But I decided to order a Mobal SIM card https://www.mobal.com at the last minute, and I was glad I did. I inserted it right after landing, and that's it, internet was available. It worked everywhere, even on the subway. And the best part was, I didn't have to constantly run around looking for Wi-Fi. Everything was great.