Many of the accommodations around Japan do offer free Wi-Fi access for guests.
Ask the concierge desk at the hotel you are staying at or at the counter of any accommodations that you are staying at for the details.
Convenient stores and Cafes
Some convenient stores with eat-in spaces may have free Wi-Fi and some chain cafes and private-owned cafes may also have them for users.
Ask the staff when you are purchasing something for the Wi-Fi details.
Other Public Wi-Fi
Some cities in Japan offer free Wi-Fi access for visitors.