Here are some regulations for hotspot implementations in Japan that you have to watch out for if you want to deploy a captive portal in Japan.

Country
Japan

Need to notify Network Regulation Authority

Yes, need to notify with network authority

Authentication required
Not a legal requirement, but recommended by authorities.

Logs policy (duration, location & how)
Duration: 6-12 months, then delete or anonymize
Location: No recommendation
How: Identification of user (Any user ID, name or phone number), type of communication (internet usage), connection time and duration, IP address and port number allocated to the user or device connected to the Internet, location of the hotspot, amount of data (can be over a session, or over a period of time).
Do not keep the user internet browsing history

Copyright infringement
Not required. However to be reported if seen.

Logs available on government request
Yes, to be delivered on request in a secured way

Privacy
Data to be encrypted and secured against unauthorized access.