Edit:
Although there weren’t many articles in English, I found this one:
Until now, Japan had not required KYC for data-only SIM cards, which could not be used for voice calls. As a result, these cards were popular among privacy-conscious users in Japan.
However, the Japanese government approved a bill in a cabinet meeting this month that would extend KYC requirements to these cards. If passed by the Diet, the law will take effect in April next year.
This bill will primarily impact privacy-conscious users in Japan and visitors to the country.
Services such as Jmp.chat and Mysudo target Western markets and do not offer Japanese phone numbers or lines. Additionally, while Silent.link does offer Japanese lines, the weak yen has made them poor value for money for Japanese users.
Furthermore, KYC requirements are set to become stricter, even for prepaid SIM cards that visitors can purchase in Japan, which will likely make them even less convenient.
Below are links to bills and other documents released by the Japanese government. As these are legal documents written in Japanese, they may be difficult to understand without an LLM.