https://www.epo.org/en/service-support/faq/searching-patents/asian-patent-information/japan/filing-grant/can-i-request-my

Can I request that my application in Japan be published earlier than 18 months from the filing/earliest priority date?

A 1999 amendment to the Japanese patent law, which became effective on 1 January 2000, introduced an "early publication" system in Japan. Under this early publication system, an applicant may request that his patent application be laid open for public inspection within 18 months from the application date (or in cases where a priority or domestic priority is claimed, 18 months from the earliest priority date). Such early publication may be of interest for provisional protection or for claiming compensation from an infringing third party.

If you require a more detailed answer, please send us your question using the contact form.